1876.] 
Physics . 
423 
rise of something like 5 0 F. will be obtained, and this heating effedt might 
very easily be estimated to one-hundredth of the whole, while the same 
thermometer would serve for all the temperatures likely to occur in these 
islands during the course of the year. A pasteboard cover gilded on the out- 
side is made to surround the chamber, and between the lens and the chamber 
there is a pasteboard shield, with a hole in it, to permit the full rays from the 
lens to pass — the objedt of this shield being to prevent rays from the »un or 
sky from reaching the instrument. In such an instrument r, or the change 
taking place in the thermometer before exposure to the sun, will in all proba- 
bility completely disappear, while r' will be extremely small. At any rate we 
may be quite certain that — 
2 
will accurately represent the heating effedt of the sun. 
At a meeting of the American Academy of Arts and Sciences held on the 
8th March, 1876, the Rumford Medal was awarded to Dr. J. W. Draper for 
his researches in radiant energy. In presenting the medals, the President 
(the Hon. Charles Francis Adams) referred to Dr. Draper’s researches as 
follows : — In 1840 Dr. Draper independently discovered the peculiar pheno- 
mena commonly known as Moser’s images, which are formed when a medal 
or coin is placed upon a polished surface of glass or metal. These images 
remain, as it were, latent until a vapour is allowed to condense upon the sur- 
face, when the image is developed and becomes visible. At a later period he 
devised the method of measuring the intensity of the chemical adtion of light, 
afterward perfected and employed by Bunsen and Roscoe in their elaborate 
investigations. This method consists in exposing to the source of light a 
mixture of equal volumes of chlorine and hydrogen gases. Combination takes 
place more or less rapidly, and the intensity of the chemical adtion of the light 
is measured by the diminution in volume. No other known method compares 
with this in accuracy, and most valuable results have been obtained by its use. 
In an elaborate investigation published in 1847 Dr. Draper established experi- 
mentally the following important fadts : — 1. All solid substances, and probably 
liquids, become incandescent at the same temperature. 2. The thermometric 
point at which substances become red-hot is about 977° F. 3. The spedtrum 
of an incandescent solid is continuous ; it contains neither bright nor dark 
fixed lines. 4. From common temperatures nearly up to 977 0 F., the rays 
emitted by a solid are invisible. At that temperature they are red, and, the 
heat of the incandescing body being made continuously to increase, other rays 
are added, increasing in refrangibility as the temperature rises. 5. While the 
addition of rays so much the more refrangible as the temperature is higher is 
taking place, there is an increase in the intensity of those already existing. 
Thirteen years afterward Kirchhoff published his celebrated memoir on the 
relations between the coefficients of emission and absorption of bodies for 
light and heat, in which he established mathematically the same fadts, and 
announced them as new. 6. Dr. Draper claims, and we believe with justice, 
to have been the first to apply the daguerreotype process to taking portraits. 
7. Dr. Draper applied ruled glasses and specula to produce spedtra for the 
study of the chemical adtion of light. The employment of ruled metallic 
specula for this purpose enabled him to avoid the absorbent adtion of glass 
and other transparent media, as well as to establish the points of maximum 
and minimum intensity with reference to portions of the spedtrum defined by 
their wave-lengths. He obtained also the advantage of employing a normal 
spedtrum in placeof one which is abnormally condensed at one end and expanded 
at the other. 8. We owe to him valuable and original researches on the 
nature of the rays absorbed in the growth of plants in sunlight. These 
researches prove that the maximum adtion is produced by the yellow rays, and 
they have been fully confirmed by more recent investigations, g. We owe to 
him, further, an elaborate discussion of the chemical adtion of light, supported 
in a great measure by his own experiments, and proving conclusively — and, as 
we believe, for the first time — that rays of all wave-lengths are capable of pro- 
