pose, the superposition of the blue and yellow tints furnished by polarized light has lately sometimes been used, but, though the result obtained is quite correct, it may be objected that this experiment was perfectly well known to Sir David Brewster, the great modern defender of the old theory, as well as to all the physicists who were his followers; and this knowledge does not seem in the least, for more than a quarter of a century, to have weakened their confidence.

FIG. 2.

RED

Nor

would it be perfectly satisfactory if I should bring about the union of blue and yellow light by the method of revolving colored disks, as is so often done; for, when we come to analyze this latter plan, we find that it consists, essentially, in presenting yellow and blue light to the eye, not simultaneously, but by a distinct succession of alternate acts. It is true that in this convenient mode of experimenting the results are the same as in that of simultaneous presentation, but just this point again would require proof, and, in a fundamental experiment like the present, ought not to be passed over in silence. To avoid these difficulties, I have contrived another plan, which will admit of our readily grasping the whole process, and inspecting its quite simple details. We have now upon the screen two large squares of blue light, and near them are two corresponding squares of yellow light (Fig. 3), and I can readily contrive matters so that the portion of the screen which is illuminated by one of the yellow squares shall also receive the light of a blue square. This we now have, and the result, as you see, is not the production of green light, or of light whose hue at all

approaches green; the light is white, with a slight tint of pink (Fig 4). Now, in this experiment, I have obtained our white light by the actual mixture on the screen of yellow and blue light, furnished by the same two glasses which, a little while ago, when superimposed,

FIG. 3.

YELLOW YET FOW

gave us green light. The apparatus is so contrived that the glasses send toward the screen yellow and blue beams of light, but, before traveling far from the lantern, these beams are caught by this large crystal of cale-spar, and each, as you see, is duplicated. Let us pursue this matter a little further, and, to facilitate our judgment of the tints, I throw on the screen, near the colored squares, a circle of unaltered white light, for comparison. Perhaps we have failed to produce green light from the circumstance that our yellow squares were too bright; with a simple contrivance I can diminish their luminosity without altering their tint, and the rate of diminution you can easily watch in

FIG. 4.

WHITE

the uncombined yellow square. This apparatus is now acting, but though under its influence the tint of the central square changes, passing from white by a series of gradations into blue, you see that it manifests no tendency to become green. Restoring the yellow squares to their original brightness, in the same way I gradually cut down the brightness of the blue squares, and yet fail to generate any hue approaching green.

A result like this ought to shake, if not entirely destroy, our confidence in the old theory, but Helmholtz has pursued the investigation still further, and has proved, in addition, that the union of the pure yel

low and blue light of the spectrum itself furnishes not green but white light. There are also other points of almost equal importance where the old theory is at variance with the facts of Nature; some of them will be noticed further on, but, for the present, in summing up this matter, we may say that, while the old theory answers tolerably— only indifferently well for mixture of pigments on the painter's palette-it quite fails when applied with any exactitude to the explanation or study of effects of color in Nature.

SANITARY SCIENCE AND PUBLIC INSTRUCTION.'

You

BY ANDREW D. WHITE, LL. D.,

PRESIDENT OF CORNELL UNIVERSITY.

are well aware that it is not by virtue of any special claims as an investigator in sanitary science, or as a student in it to any great extent, that I now address you. But, when I was invited to speak, it seemed a good opportunity to make one more point in behalf of certain great, manly studies in our system of public instruction, and especially in our institutions for advanced instruction, and therefore an opportunity not to be neglected.

The generations that come after us will doubtless wonder at what this age has done, but I think they will wonder far more at what it has not done. There will be wonder at discoveries, inventions, reforms-at all our conquests in the realms of mind and matter; but I think the wonder will grow when notice is taken of the utter neglect, in great systems of education, of the most important subjects which occupy us, either for material purposes or for mental and moral advancement. Look, first, at the neglect of political studies. Here is a great Republic, dependent, as all confess, upon the knowledge of those who live beneath its sway. And yet you may go from one end of the country to the other and hardly find the slightest provision for any real instruction in Political Science, whether it be in political economy or political history. If, during the war of our rebellion, any thoughtful American wished to find out what that history was in which the germs of that great struggle were planted and developed, he had to go for such knowledge to the public lecture-room of Laboulaye at Paris, or the private lecture-room of Neumann at Berlin.

The case is still worse in regard to that great class of studies comprehended under the designation of Social Science. Every year our national Legislature and some forty State and Territorial Legislatures, and a vast number of county and town boards, are brought face to face with the most vital social problems. They are called upon to

1 Read at the recent meeting of the American Public Health Association.

make great expenditures for the prevention and cure of pauperism, for the repression and punishment of crime, for the treatment of lunatics of various sorts, for the care of idiots of various grades, for the special treatment of inebriates, for the cure of the sick in hospitals, for general measures of prevention, as regards epidemics, and yet no one will gainsay my assertion that on no subject are our Legislature, and all our various public bodies, so utterly blind as on this. If we look at the result of this as regards expenditure, the case is bad enough. The amount annually expended in all our States for this purpose is enormous. The only approach which we have to the palaces of the Old World are in the various hospitals and prisons and asylums of the New. I can speak of this want of knowledge from personal experience. I can stand in the confessional on this subject. It has been my lot more than once to vote on such appropriations in a legislative body. I remember especially one case where the Legislature of this State was called upon to establish a great asylum, at vast expense, for a certain class of lunatics. The case was very pressing. A careful report from a commission showed that some provision of this sort must be made. A bill was passed, the buildings were erected, and yet, when all was done, we were assured by an expert, who had no interest one way or the other in the matter, that all our well-meant benevolence had, perhaps, resulted in almost as much evil as good, and that the whole institution was a failure as regards the immediate purposes for which it was erected. The simple cause for this was that in that whole Legislature, in the lower House, in the upper House, in the Executive Department, there was not one person who had ever given any close attention to subjects of this kind, and we had been obliged to trust entirely to those who could give us scraps of information, no matter how crude. But, if the immediate results are unfortunate, the remote results are still more so.

If any one wishes to see what vicious methods of dealing with great social questions will produce, he has only to look at the great harvest of evil which England is now reaping from seed sown 300 years ago, especially as regards the treatment of her pauper and criminal classes. I have said that there is no provision for thorough instruction. The reason is twofold. The first is the reluctance of educators to take up new subjects of study, or, at least, to present them thoroughly. But the other and far more effective reason is the fact that we have so few institutions for advanced education which have the means to make provision for such teaching. The last report of the Commissioners of Education at Washington shows that we have in this country about 400 establishments calling themselves colleges or universities. You may count on your fingers all those which really have any claim to either title. In obedience to the demands of sect or of locality, we have gone on multiplying institutions insufficiently endowed, wretchedly wanting in every thing necessary to scientific

investigation, until we have now hardly three or four in possession of the means to present any new subject of study involving any outlay for investigation or for demonstration. The time has come when such provision should be made. Whether it is to be made by the munificence of private individuals, or by State endowments, is not here the question.

The proposition to which I shall speak especially is this: that provision should be made for instruction in Human Physiology, Hygiene, and Sanitary Science, in all departments of public instruction in our public schools, by providing fundamental instruction, especially in the simple principles of physiology and hygiene; in colleges and universities, by presenting this general instruction in a more extended way, and by promoting investigation; in medical colleges, by giving more special instruction in matters relating to public and international hygiene; and that, in our departments of engineering and polytechnic and technological schools, especial provision should be made for instruction in sanitary engineering.

In regard to the first of these provisions, that for popular instruction, few probably are aware of the need of them. Take, for example, the revelation made within the past year, at the outbreak of yellow fever in a Southern city. Two things in relation to that revealed very clearly the evils of which I speak: First, the cause assigned to the disease shows the utter want of sanitary knowledge in the people at large; and, secondly, the real cause, since revealed, shows the absolute blindness to the simplest principles of sanitary science on the part of those immediately concerned. When the yellow fever broke out at Shreveport, it was telegraphed all over the country that it was caused by the removal of the obstructions in the river above the city. That statement went all over the country unchallenged. So far as I know, no one thought of expressing doubt publicly as to the statement that the yellow fever was caused by a more plentiful supply of water at the wharves of that city-the fact being that this would conduce rather to the removal of the causes of the disease than to the prevention of them. At last came information as to the real cause, and it was found that in that hot climate men had been allowed to heap up the material in which disease-germs arise abundantly; that the simplest truths of sanitary science had been ignored, and that the consequence was perfectly simple and natural.

But it is not merely in such outstanding parts of the nation that such ignorance exists. It is spread throughout our own country districts, even the most enlightened districts, and you will find prevailing in many of our country towns traditions and superstitions in regard to this matter that are most surprising. You will find some of these things which are known to be absolutely deadly considered on the whole as healthful. Strange as it may seem, you may hear people who take the papers, who are supposed to be within reach of the great