has been thought of and mentioned, the facts they have recorded have been collected more for the benefit of commerce than agriculture, and in the latter connection, they are, as we have said, sadly deficient.

Count de Gasparin seems to have been the first to call attention to the relations we have mentioned, and he has had at least two active followers, Quetelet in Belgium, and Marié-Davy in France. The sentiments of the latter in this particular are ably embodied in the prelude to an article in the Journal d'Agriculture Pratique of last year, in which he says, "Agriculture and its products have thus far received comparatively little profit from the labors of meteorologists, because the latter have been more preoccupied with questions of climatology in general, than with agricultural climatology, and the data they discuss, look to the first and not to the second." This difficulty belongs to all countries alike—Davy himself is making an excellent start in the right direction, at the Observatory of Montsouris, and he has already secured results of great scientific and practical value; but in order that his plan of work may be attended with the most fruitful results, he should have more extended coöperation, and the observations he makes and records should be made at a large number of stations, to render accurate generalization possible. He observes and records all the conditions we have named. In this country, we have nothing comparable with it.

Our Signal Bureau, probably the most perfect of its kind, for the purposes for which it was designed, renders excellent service to agriculture and commerce, and we would not question its efficiency; but its work, as it claims, tends to the commercial rather than to the physiological side- to predictions of future conditions which may affect human affairs, rather than to the record and discussion of the effects of conditions which have existed, upon the development of crops. Nor is its organization sufficiently extensive to effect the end we have in view, the whole number of observers engaged under its direction, not being more than 800; while for practical deductions, for agricultural work, 3000 for the United States would not be excessive. But I believe the machinery and organization of the Department of Agriculture could be employed with good effect in this connection, and the desired observations for this country secured, through the 2300 observers and reporters it already employs to make monthly returns concerning

the condition of the crops, and who receive, as compensation for their services, the publications of the Department. If the necessary instruments were supplied them, it would doubtless be found that very few would decline to perform the tasks requested at their hands-making the observations and reporting weekly or monthly records to the Department, where their results could be tabulated and discussed in connection with their simultaneous returns of the condition of the crops.

I have, therefore, taken the liberty to suggest to Gen. Le Duc, the Commissioner of Agriculture, the following plan of work in Agricultural Meteorology for his Department, and I am pleased to say that he fully recognizes its necessity, and is in full sympathy with it, though he would, of course, require congressional support to enable him to carry it out.

The plan is this:

1. The establishment of a system of observation and record among the reporters to the Department, and others whose cooperation may be secured throughout the United States and Territories, with instruction to observers to keep careful records of the conditions of atmospheric pressure, temperature in its various relations, relative humidity, evaporation of moisture, winds, light, tension of atmospheric electricity, occurrence of dews, fogs, and frosts, and report them at stated intervals of time to the Department for consideration and permanent record.

2. The collection of meteorological records from every part of the world, from which to construct detailed tables, showing the relations of all the conditions named above, and that may influence the growth or health of vegetation.

3. The construction of maps showing the geographical distribution of various crops to be used in connection with the meteorological or climatic data to be collected.

To secure the data from abroad for this work, correspondence should be established with ministries of agriculture of foreign governments, learned societies, institutions of learning and research, and students in meteorology and allied sciences, requesting information concerning the published and manuscript records of each country and sources from which copies of them can be obtained. They should then be secured to facilitate the end in view. Information should also be requested concerning the cultures to which each country is devoted, those which succeed

well and are profitable, and those which have been experimented upon with unprofitable financial results.

In the tables and maps that could be constructed from the information thus gained, there would be found an almost perfect guide as to experiments that may be made in new cultures with prospect of success. Such work would in no way interfere with that of the Signal Bureau, the value of which cannot be overrated - and on account of the very nature of the work, it should be carried on by the Department of Agriculture. It would become an additional source of knowledge concerning that science in which all classes of the people are equally interested, and if the knowledge thus gained be applied to the management of farm crops, it will be difficult to estimate the saving that must result in the expenditure of time and means, and of enterprising and intelligent labor of agriculturists often employed in unfruitful experiments that could be directed to other channels of industry, or other and profitable cultures.

THE ACTION OF SUNLIGHT ON GLASS. BY THOMAS GAFFIELD, of Boston, Mass.

WHEN God made the light, He created one of the most ethereal and yet most powerful of the elements and forces of nature.

It will be my pleasure to show how the sun, its great fountain and source, while it paints so beautifully and wonderfully the birds, the insects and the flowers, can in some measure also delicately tint the wares upon our tables, the glass in our houses, and the windows of the storied cathedrals of the world.

My subject is the action of sunlight in changing the color of glass, and I shall give a brief account of my humble experiments, commenced in 1863, and continued to the present day.

There is no mention of the subject in ancient records, for there was little need or use of glass windows in the olden time, and probably little or no glass of composition or color liable to any very perceptible change of tint. Not until after the beginning of the present century was the phenomenon observed in Europe, in the change of some light colored plate glass to a purple and of

another kind to a yellowish hue. In 1823, and the following year, Faraday, Bontemps and Fresnel made a few brief experiments showing that exposure to sunlight effected this change of color.

Other experiments were made by Melloni and Hunt, showing the action of glasses of different colors as media in the transmission of light and heat, but none to my knowledge are recorded up to 1863, with the above exceptions, showing the effect produced on the glass itself. The observations upon the subject by Pelouze (who for many years was the chemist of the French Plate Glass works at St. Gobain) are published in the Comptes Rendus for January 14, 1867.

Without making any pretension to the learning of the schools, or accurate scientific knowledge, I believe that my experiments, suggested by my experience as a glass-dealer and manufacturer, are original in their method and extent, as they cover the whole field of glass-making, including both colored and colorless glass. Those in connection with colored glass are entirely new.

By colorless glass is intended glass like that which we see in our windows, which shows little or no color in looking through its surface; but, observed through the edges, exhibits a great variety of tints, running from the almost colorless white to those of yellow, blue and green. The really colored glasses-made so intentionally by the addition of some metallic oxide, or other coloring constituent can only be observed through the surface, as their opacity, except in the lightest colored specimens, will not allow an observation through the edges for more than a fraction of an inch. My experiments have been carried on chiefly upon the roof and upper window-sills of my house in Boston, in a position exposed to the full force of the sun's rays during the greater portion of every day, being protected by covers only in the event of snowstorms. Of course, a perfect arrangement could only be made when a flat roof or platform in an open field could be provided, and the sunlight could act with full force during every hour and minute of the day.

But mine was sufficiently near this point to show very interesting results. The change in color in some specimens is developed slowly, while in others it commences after a few hours of exposure in a summer day. In some sensitive kinds, I have witnessed a perceptible change in a single hour of sunlight exposure upon the top of a post in a country garden, at noontime, on a clear and hot day of August.

The glass plates exposed vary from four by two inches (my usual size) to four by eighteen, and from one-sixteenth of an inch to an inch in thickness. I have in my cabinet more than a thousand specimens showing the effect of exposure from a single hour to thirteen years.

I have thus exposed and tested some eighty kinds of colorless glass of American, English, French, German, and Belgian manufacture; embracing rough and polished plate; crown and sheet window glass; flint and crown optical glass; glass ware and glass in the rough metal. I have also exposed ground and opal glass, and some seventy kinds of colored sheet and rolled cathedral glass, including not only the main spectral colors, -red, orange, yellow, green, blue and violet,-but a variety of intermediate tints, such as brown, olive, amethyst, flesh color, etc.

I cannot in these brief moments give you all the privately recorded details of the interesting results of these experiments; but referring you to Silliman's Journal for 1867, for an account of the same up to that date, I shall rather hasten to allow my illustrations to tell their own story, which they will do without any color of exaggeration.

Various are the tints of the original colorless specimens, and equally various are those which are produced by sunlight exposure. The nomenclature of different observers might also vary. I cannot recapitulate the long list from my journal, but would name as a general classification of the results produced, the following changes of color:

1. From white to yellowish.

2. From greenish to yellowish-green.

3. From brownish-yellow and greenish tints to various tints of purple.

4. From greenish-white to bluish.

5. From bluish and other tints to darker tints of the same colors.

Every specimen of colorless glass exposed for ten years has changed in color or tint, except some white flint glass, such as is used for fine glass-ware and optical glass. The optical glasses exposed-with the exception of two specimens of crown glass, containing no oxide of lead, which became of a yellowish hucchanged only in a very slight degree in tint, even after more than ten years of exposure, and not enough to be witnessed by ordinary