It will not I hope be considered improper if I venture (entirely, of course, on my own responsibility), to make some remarks with the view of aiding those who are not botanists to form an opinion upon the matter.

In the first place it may be well to give some notion of the nature of a public herbarium and the purposes it serves. Most persons are aware that with a little care specimens of almost any plant can be dried under pressure, so as to give, even to those who are not accustomed to study such specimens, some notion of what the plant is like in the fresh state. To a professed botanist they yield of course a great deal more information.

A herbarium then consists of a collection of dried plants. Whatever may be the plan adopted by private individuals, it is absolutely necessary in a public herbarium that the specimens should be securely stuck down upon sheets of paper, in order that they may bear frequent handling without injury. This does not, however, prevent the detachment under proper supervision of such fragments as can be spared and are requisite for scientific investigation. The sheets on which the specimens are fastened are placed in loose covers, and these are arranged in proper classificatory order on the shelves of cabinets which are made to hold them.

Any botanist interested in any particular group of plants, and visiting a well-worked herbarium, has only to go to the proper place to find everything that the herbarium contains belonging to that group ready to his hand, and in a state suitable for study. Such a result is not, however, attained without immense labour on the part of those who have charge of the herbarium. Fresh accessions of plants have continually to be examined in detail before the proper positions for their intercalation in the arranged collection can be determined.

A public herbarium derives its additions from three sources-gifts, exchange, and purchase. The first includes, besides collections given by the government departments, at whose instance they have been made, supplies coming from private individuals. At Kew the Garden and the Herbarium benefit in common by the extensive correspondence carried on in every part of the globe with persons of every grade. Contributions, both large and small, are constantly arriving of living and dried plants, seeds, and specimens unsuitable for herbarium purposes but which find their place in the Museums. This correspondence it has required a long period to organise, and it needs no small exertion to continue and extend it. I conceive that it is, putting aside all others, a very strong argument for the maintenance of a herbarium at Kew, that it participates, as no other herbarium in this country could do, in the results of a correspondence which must necessarily be kept up for the purposes of the Garden, and which indeed could hardly be carried on elsewhere for the advantage of a herbarium alone, to anything like the same extent. Moreover the correspondents of Kew constantly send dried plants to be named, besides making demands for every kind of information which nothing but a herbarium and library on the spot could enable them to be supplied with.

The dried plants which are received at Kew from different sources necessarily include a large number of duplicates, that is, of specimens not needed for the herbarium. These, however, are not wasted, but are sent from Kew to various establishments with which exchanges can be effected. This is a most important matter, because the authentically named specimens of foreign botanists which are received in exchange are far more useful for purposes of comparison than any figures or descriptions.

The uses of a large herbarium are in the main two. In the first place it supplies the material for purely scientific investigations, both with regard to the structure and classification of plants as well as with regard to their geographical relations and the problem of how their world distribution has come to be what it is. But a herbarium

is also most important on purely utilitarian grounds. An immense number of important products are derived from the vegetable kingdom, and it is very necessary to have exact and precise information as to the plants which produce these. Dried plants preserved in herbaria are standards of reference in comparison with which the names of specimens can be accurately determined. Botanical names have a universal currency, and therefore obviate all the divergencies and confusion of those which are merely local and vernacular. Horticulturists moreover look to those who have access to herbaria to guarantee the correctness of the nomenclature of garden plants.

Besides the herbarium at Kew there is the older one belonging to the British Museum. It is still in a measure sub judice what is to be the future position of these two institutions. That the Kew Herbarium should not be severed from the Garden is the all but unanimous judgment of those who are best qualified to give an opinion. With respect to the British Museum Herbarium there is greater difference. Some botanists have wished to see the valuable type specimens which it contains added to those at Kew, just as they might wish, if it were in their power, to condense there what is best in some of the leading foreign herbaria. In my opinion the transference to Kew of any portion of the British Museum collections would be very undesirable. The British Museum specimens are mounted on paper of a very different size, and the sheets could not be cut down without impairing their authenticity. Moreover, at the British Museum there is an extensive series of ante- Linnean herbaria most valuable from a historical point of view, but not otherwise available for study, and these would, on that account, be out of place at Kew. Again, with collections so combustible as those of dried plants, it is all but imperative to divide the risk of losing the whole national accumulations in one conflagration.

The two Herbaria have also two well-marked but distinct fields of activity open to them. Let the Kew Herbarium remain, as at present, to be used for the varied ends of the Kew establishment, and by such students as are engaged in important works, as original memoirs and colonial or forest floras executed for the Government. They would be willing to gain, as they do now by the distance from town, tranquillity from the incursion of visitors less permanently occupied with botanical pursuits. Then the British Museum collections (which, if it were possible, it would be a convenient arrangement to retain in Bloomsbury) would serve still for persons who would use them rather for reference than for continuous study, although this also would not be precluded. It must, however, be admitted that they are capable of very great improvement even for purposes of reference, and it would be very desirable to this end that the Kew and Bloomsbury establishments should be brought into some sort of amicable relation. I will give a few instances quite arbitrarily selected from my own experience, which will show how very far behind the British Museum Herbarium is in completeness to that of Kew.

The Indo-Malayan genus Dipterocarpus is represented in the former by 17 sheets, including to species, in the latter by 116 sheets, including 31 species; the South African genus Stapelia, consisting of plants very difficult to dry, in the former by 4 sheets of 3 species, in the latter by 48 sheets of 25 species; lastly the Tas nanian Athrotaxis (Conifera), of which one specis is to be found in nurserymen's catalogues, is represented at Kew by 16 sheets, illustrating all the three known species; while at the British Museum I have not succeeded in discovering a single specimen in the arranged collection at all.

But a very large portion of the plants at the British Museum are practically inaccessible. Unfastened on paper, and much in the state in which they were received from the collectors, except a rough geographical distribution into

cupboards, they are little more assorted than the plants which constitute a haystack. A considerable part, if not the whole, of the 7,000 specimens of plants from the expeditions of Hooker and Thomson, which cannot have been received less than fifteen years ago, were, quite lately, still unmounted and unincorporated. Again, merely to quote instances which have come unsought within my own observation, the plants collected in Nepaul half a century since by Wallich, and as I learn from a distinguished Indian botanist, in a district which has never since been botanically explored, were recently, and perhaps are still, amongst the unarranged collections. These altogether, I should judge, roughly form in bulk about one-sixth of the whole herbarium. The arranged portion is estimated to possess 77,400 species of flowering plants, contained in 306 cabinets with 8 shelves; the Kew Herbarium, on the other hand, possesses 105,000 to 110.000 species in 450 cabinets, on an average of 16 shelves. As I have ascertained that the shelves are in each case about the same width apart, and about equally filled, these figures give roughly three times as many shelves to the Kew Herbarium, and somewhat less than half as many more species.

There can be no doubt, therefore, that the British Museum Herbarium might be materially developed, especially when it is remembered that Mr. Bentham's herbarium, when presented to Kew, contained between 60,000 and 70,000 species, and that this was formed in less than forty years by a single individual. The examination of the unarranged collections in the British Museum would, no doubt, yield a large number of duplicates, and these should be exchanged with foreign herbaria. If this were done-and there is no reason why the appliances of Kew should not be utilised for the purpose-it would be easy, without interfering with the independent action of either establishment, to bring about for the future a mutual interchange of specimens. Nor is there any reason why, when needful, the type specimens of the older botanists should not be lent to Kew from the other Herbarium, considering that both are Government property.

The development of the botanical collections in the rooms open to the public at the British Museum into something more useful, educationally, would probably be achieved by the officers, if they possessed more space. In this case it would be very desirable to transfer to them the collections belonging to vegetable palæontology in the Geological department. At present the nucleus of a collection of fossil plants bequeathed to the Botanical department by Robert Brown is being gradually developed, so that there are now actually two distinct collections, both having the same object, and existing independently of one another, and in charge of different officers, in the same building. W. T. THISELTON DYER

and November were very wet months,--all these months being characterised by a small rainfall in the north.

The mean temperature at Stykkisholm, in the northwest of Iceland, was 33°7 in January, or 68 above the average, being the highest mean temperature recorded in January since 1846, except that of 1862, which was 1°0 higher; 5207 in July, and 51°6 in August, being respectively 3° 6 and 3°4 above the average of these months, and the highest that has occurred since July 1847 and August 1846. And as June was o°6 and September 10 above the average, the past summer has been one of the finest experienced in Iceland for many years. The temperature in April was 3°5, in May 14, and in October 10 under the average. On the other hand, the temperature of Faroe closely agreed with that of Scotland during the year, viz., above the average in January, February, March, April, June, July, and November, and under the average during the other months, especially September. At Melstadt, on the north coast of Iceland, the summer was very fine, but in the beginning of October the weather broke, and on the 13th the temperature fell to 3°0 or 29°0 below freezing. At Reykjavik, the summer was also fine, but the autumn was remarkable for north and north-east gales, frequent auroras, low sea temperature, and large amount of ozone. Along with the unusual manifestation of these phenomena, inflammatory diseases were prevalent, especially bronchitis, catarrh, croup, and diphtheria.

The temperature of the sea presented certain very interesting anomalies during the year. In the earlier months it was, equally with the temperature of the air, above the average of former years in Iceland, Faroe, and Scotland. But at Stykkisholm it was 2°7 in May, and 4°2 in June below the average, it being at the same time from half a degree to a degree above the average in Faroe and Scotland. On the other hand, the sea was, at Stykkisholm, 2°8 in August, and 2o6 in September above the average, whereas at Sandwick, Orkney, it was 12 and 11 below it in the same months. In Faroe the temperature of the sea was above the average every month of the year (except October, when it was o°3 below it), amounting during the eleven months to an average excess of 1°1.

The following are the differences from the averages of the sea temperatures at Stykkisholm from March to October, 1872:

In May the mean temperature of the sea was 36°7, and in August 53°1. So great an increase as 176 has not been previously observed in these months.

It is also a noteworthy circumstance that the means of the nine months' barometric pressure, from February to October, at Stykkisholm, have been in every case above

NORTH-WESTERN EUROPE

HE Scottish Meteorological Society have just received

THE

letters from their observers in Iceland and Faroe, together with the regular observations made by them for the Society to the end of November last, which are of interest in connection with the unprecedentedly wet and changeable season we have had in Scotland and elsewhere.

The rainfall in Iceland this year to the end of October has been 44 inches under the average of the ten months, the deficiency occurring chiefly in January, February, July, September, and October. In Faroe the deficiency has, to the end of November, amounted to 100 inches, the dry months being February, 4 50 inches under the average; July, 1'09 inch; August, 2'97 inches, and November, 4'17 inches. In Scotland, February was everywhere a wet month, except in the northern and western islands and in Clydesdale; and September, October,

o'118 inch. In Norway also, from February to August, to which the observations have reached us, the means were every month above the average, amounting at Vardoe (lat. 70° 20') to a mean monthly excess of o260 inch; Christiansund, o'129 inch; Christiania, o'151 inch; and Maudal, near the Naze, o‘084 inch. On the other hand, barometric pressure was every month from February to October, below the average; at Paris, and in Gue nsey, the mean monthly deficiency being respectively o'074 and o'090 inch. At Greenwich, the mean deficiency for the last nine months was o'083 inch; Glasgow, o'091 inch; Edinburgh, o'o88 inch; Aberdeen, o'072 inch; Culloden, near Inverness, 0'34 inch; aud at Sto noway, the station nearest to Iceland, only o'006 inch. This high barometer in Iceland and Norway has had an important bearing on the unprecedently wet weather, and the accompanying low barometer we have had south of that region.

ALEXANDER BUGHAN

IN

ON THE SPECTROSCOPE AND ITS APPLICATIONS

IV.

N what has now been stated we first saw Newton founding spectral analysis, by using a hole in a shutter and a prism; then we discussed Wollaston's substitution of the slit; after that Mr. Simms' introduction of the collimating lens was referred to; and then the growth of the modern spectroscope.

It is time, now, that we came to the applications of the instrument. And in dealing with these applications I shall divide my subject into two perfectly distinct portions. I shall first deal with those which depend upon the different modes in which light is given out or radiated by

be present. If I were to burn a piece of paper, or a match or an ordinary coal gas flame, you all know we should get a white light, but you may possibly not all know that if we raise any solid or liquid to a state of incandescence or glowing heat we should get exactly that same sort of light, which will always give us a continuous spectrum. Before a large audience the best method of showing this fact is to use an apparatus called the electric lamp, and to pass the current of electricity through two carbon points, which are intensely heated by their resistance to the passage of the current. The spectrum obtained from these points, by means of the dispersion of two bisulphide of carbon prisms, is quite continuous from end to end. Now carbon is a solid, and therefore if we take carbon as an example of a solid or liquid substance in a state of vivid .incandescence, and we obtain from these carbon points a continuous spectrum, you must accept that as an indica

FIG. 9-Electric Lamp.

various bodies under different physical conditions, with, in fact, the radiation of light. And, in the second place, I shall deal with the spectroscope's story of the way in which white light giving a continuous spectrum is stopped or absorbed by different transparent bodies-with in fact the absorption of light.

The first application of this question of radiation is one cf the most general importance. It enables us to differentiate between solid, liquid, and gaseous substances, and between gaseous or vaporous substances in different stages of pressure. If, for instance, we take a platinum wire and heat it to redness, and examine by means of the spectroscope, the light emitted we shall find that only red rays are visible, then if the wire be gradually heated more strongly, the yellow, green, and blue, rays will become visible, until finally when the wire has attained a brilliant white heat, the whole of the colours of the spectrum will

FIG. 20.-Arrangement of the electric lamp used for rapid comparisons. tion of the truth of what I say, for I have not time to experiment on every solid and every liquid substance. The spectrum is received on the screen, and you see it is continuous, that is to say, there are no breaks, such as those we saw in the figure representing a portion of the solar spectrum on page 167 where the black lines represent the breaks in the solar spectrum which are called the Fraunhofer lines.

Let us then consider this fact established, namely, that solid or liquid bodies, when heated to a vivid incandescence, give a continuous sprectrum without bright lines. Under these circumstances the light to the eye, without the spectroscope, will be white, like that of a white hot poker; if the degree of incandescence is not so high, the light may only be red, like that of a redhot poker. But so far as the spectrum goes-and it will expand towards the violet, as the incandescence increases, as before stated-it will be continuous.

Now, suppose, instead of giving you the spectrum of

bustion due to the greater supply of air from the holes at the bottorn. The flame immediately becomes of an intense yellow colour due to the vapour of sodium. In this we have further evidence of the connection between the colour of the light which we get from a vapour and the spectrum of that vapour. It is usual to place the salt to be examined in a platinum spoon, and insert it in the flame, but the utmost constancy is insured by adopting an arrangement of Mitscherlich's shown in the accompanying drawing, (Fig. 24) in which a platinum wick is kept continually moistened by a solution of the salt, generally the chloride, the spectrum of which is required to be examined. You will imagine, à priori, from what I have already said, that as in the case of sodium vapour, the colour of the light is orange, the line of the vapour will appear in the yellow or orange part of the spectrum, and

FIG. 24.-Geissler's tube, showing electric discharge.

you will not be mistaken. For you will see on examining this flame with a spectroscope, that we obtain a spectrum consisting of a brilliant yellow line upon an almost black background; if, however, the flame is observed by means of a very narrow slit, this line will appear double, that is it really consists of two extremely fine lines which are very close to each other, and if the slit be wide the images overlap one another.

If we then pass on to another substance, and take some lithium instead of sodium, we obtain a brilliant carmine tinted flame, which on examination by the spectroscope, is found to give a spectrum consisting of one splendid red, and a fainter orange line. Potassium gives a violet coloured flame, and yields in the spectroscope a red line and a violet line. If, again, we take a salt of strontium, which was one of the ingredients in red fire, it colours the flame crimson, and by the eye the flame can scarcely be distinguished from the colour of the lithium flame, but in the spectroscope there is no possibility of doubt, the spectrum of strontium, consists of a group of several lines in the red and orange, and a fine line in the blue end of the spectrum.

If a higher temperature than that of the Bunsen flame is required the blow-pipe flame may be resorted to; in this, the quantity of air and coal-gas is varied at pleasure, and a very high temperature may be obtained.

We might proceed thus to examine all the elementary substances one by one, but to observe the spectra of the metals, it will be found necessary to use a higher temperature still, and for this purpose the electric arc or spark is employed. If a temperature only slightly greater than that of the blow-pipe flame is used, the spark from an induction coil worked by five Grove cells may be taken as shown in Fig. 21, the Leyden jar not being employed; a few metallic lines will then be seen, and a background consisting generally of bands of light here

and there.

If a higher temperature still is used, the jar may be thrown into the circuit, upon which the spark will become more intense, according to the power of the coil and size of the jar; or the electric arc may be employed. The spectra

thus obtained are much more complex; the spectrum of iron, for instance, when examined at this high temperature, is found to consist of no less than 460 lines, many of which are situated in the green part of the spectrum.

With regard to solid and vaporous bodies, the electric lamp affords a very handy method when properly employed, of examining and exhibiting the spectra of these bodies to large audiences.

But there are a great many gases which the spectroscopist also has to study, and to study with the greatest