APPENDIX V. REPORT OF THE OPERATIONS OF THE ASTROPHYSICAL OBSERVATORY FOR THE YEAR ENDING JUNE 30, 1905. SIR: The equipment of the Astrophysical Observatory is now valued as follows: Buildings Library and records_ $7.400 45.300 7,200 The fence around the ObBy permission of the park same time enlarged on the During the year three wooden shelters, covering, respectively, the cœlostat, the long focus concave mirror, and the bolographic outfit for observing the solar image, have been erected at a cost of $1,135. This item is chargeable to the appropriation for the fiscal year ending June 30, 1904. servatory lot has been renewed at a cost of $554. authorities the Observatory inclosure was at the east and south, and now contains 15,300 square feet. Apparatus chiefly for use in a proposed expedition to a high altitude observing station has been procured at a cost of $3,862. Of this sum, $2,527 is chargeable to the appropriation for the fiscal year ending June 30, 1904. Usual periodicals have been continued, a few books of reference have been purchased, and about 118 volumes have been collated and bound, at a total cost of $369. No losses of property beyond usual wear and tear have occurred during the year. Changes in personnel.-In the latter half of 1904 Dr. S. A. Mitchell was employed three months as temporary assistant on stellar radiation experiments. Richard Norris resigned March 31, 1905. By request of the Chief of the Weather Bureau Mr. H. H. Kimball was assigned to the Observatory temporarily for a period beginning May 1, 1905, in order that he might learn the methods of bolographic observation employed here. Mr. L. R. Ingersoll was engaged for three months, beginning May 10, 1905, as temporary assistant for the Mount Wilson expedition. Joseph Dwyer, messenger, was engaged April 1, 1905. WORK OF THE OBSERVATORY. For convenience I describe the work of the Observatory under the following headings: (1) Observations at Washington on the variability of the sun. (2) Miscellaneous work. (3) Expedition to Mount Wilson in California. (1) OBSERVATIONS AT WASHINGTON ON THE VARIABILITY OF THE SUN. As indicated in your paper, “On a possible variation of the solar radiation," a and summarized in my last year's report, our observations of several years, but especially of the year 1903, have tended to produce the belief that the total radiation of the sun may vary in comparatively brief periods, these variations of solar radiation being irregular in period, but tolerably frequent a Astrophysical Journal, June, 1904, and London, Edinburg, and Dublin Philosophical Magazine, July, 1904. 74 and large enough to produce considerable changes of the earth's mean temperature. During the past year the work of the Observatory has been chiefly directed toward testing the supposed variability of the sun and increasing our knowledge of it. As I have said in my last report, this investigation has three main branches as follows: First. The determination of the intensity and variation of the total solar radiation reaching the outer limit of our atmosphere. Second, the examination of the distribution of solar radiation over the sun's disk for the purpose of detecting changes of absorption in the solar envelope. Third, the reduction of temperature measurements from numerous meteorological stations to note departures of the temperature of the earth from its mean. General view of the results thus far obtained since January, 1902. Before reporting fully this year's work I give in the accompanying chart, Plate V, a general view of the results of the last two and a half years touching this question. Three series of observations are represented in the chart, namely: A.. Average departures from mean temperature for 89 stations distributed over the North Temperate Zone, represented by the full line at the top of the diagram. B. The transmission of the solar envelope for radiations of wave length 0.50μa (green), as computed from spectrobolometric observations of the sun's disk at Washington, represented by the line at the middle of the diagram. C. The solar radiation outside the earth's atmosphere as computed from spectrobolometric observations at Washington, represented by the lower line of the diagram. As the observations of type B and earlier ones of type C are frequently separated by long intervals of time, the lines connecting the points should not be interpreted as necessarily indicating the intervening values of the quantity observed. Observations of the solar constant taken in Washington are seldom of a satisfactory character, owing to the scarcity of days when uniform transparency of the atmosphere persists for the several hours required for the determinations. Accordingly only a few of the observations of type C are entitled to great weight, and these are designated in the diagram by the letter G to denote it. Observations of good character, but less satisfactory than these first, are designated by M, denoting medium weight. A still less perfect class, to which, unfortunately, most of the observations of 1904 and 1905 belong, is designated by the letter L, signifying of little weight. Some observations still less satisfactory than these I have omitted from the diagram as deserving no weight at all. Considering now the diagram it will be seen that early in the year 1903 there was a long-continued period of abnormally high terrestrial temperature, and this was followed by a still longer period of abnormally low temperature. Corresponding well with this state of affairs are the observations of total solar radiation, and these observations are fortunately almost all of great, or at least medium, weight. In September, 1903, a single observation of the transmission of the solar envelope was made, and this, compared with others of more recent date, is low, indicating that diminished transparency of the solar envelope was the probable reason for the small amount of radiation and low temperature observed at the same time. In the year 1994 there was no long-continued period of abnormal temperature Results of a similar trend are obtained for all wave lengths, and this wave length is chosen merely in illustration. departure comparable with those noted in 1903. So far as there were notable variations from the mean in the temperature of the North Temperate Zone, these occurred in January and February, and in October and November of 1904. On the whole, these departures are confirmatory of the indications of the spectro-bolometric determinations of total radiation for the same periods, but these results, owing to scarcity of good weather, are lamentably inadequate. Still, a medium-weight observation of June indicates average temperature and is followed by it; a first-class observation of October 5 indicates high temperature and is followed by it, and a medium-weight observation of October 22, indicating low temperature, is followed by it. Prior to December there are only two observations of solar transmission, of which the first, a high value, comes just at the end of a period of high temperature, while the second, a low value, in November, comes just preceding a short period of low temperature. In December higher values are found and higher temperatures follow. The temperature departures of the first half of 1905 also present no such favorable opportunity for comparison with solar radiation phenomena as was presented in 1903. The data on total solar radiation have not been fully reduced as yet, so that they appear still more meager than in former years, and more so than they will after all returns are in. But the weather seldom permitted satisfactory solar constant determinations at Washington in the first half of 1905. Those observations here given fall in fairly well, as will be seen, with the record of temperature departures. Observations of the solar transmission have been made very frequently since December, 1904, and are as a rule nearly average values and indicative of average temperatures, and thus in accord with the facts for the North Temperate Zone. Increasing values in December and January and diminishing ones in February and in April and May have their counterparts in the temperature curve for the North Temperate Zone. The temporarily lower values in June find no counterpart in the temperatures of the North Temperate Zone, but a fall of temperature may possibly be shown early in July. Taking all the facts together we find high values of solar radiation and solar transmission preceding and accompanying high temperatures of the North Temperate Zone; low values of solar radiation and solar transmission preceding and accompanying low temperatures of the North Temperate Zone, and intermediate values of these solar phenomena accompanying intermediate terrestrial temperatures. The evidence at hand is still too fragmentary to produce full conviction, but subject to later confirmation or rejection, as further work shall prove, the results obtained thus far strongly indicate that the transparency of the solar envelope varies at irregular intervals, with consequent fluctuations of the solar radiation transmitted to the earth, and that this in turn affects the mean temperature of the earth. Observations of 1904-5. (a) Solar constant work.-Determinations of the radiation reaching the earth's surface, both in toto and for separate wave lengths, have been made at all times when conditions permitted, and have been reduced as in former years to give the transmission of our atmosphere, and the total radiation reaching its outer limit. As above stated the number of days when the sky has continued satisfactorily uniform for this purpose have been few, and besides owing to the press of observing and computing work it has not been possible to compute all the results as yet, so that on both accounts the tables which follow are more than usually meager. Table 1 gives in continuation of similar tables in preceding reports the transmission of the atmosphere at various wave lengths for vertical rays. |