Page:Popular Science Monthly Volume 15.djvu/143

Rh results which he reached were at once accepted as valid advances in the fields of Physics, Chemistry, and Physiology. But, in regard to the study of the radiations and the new results attained in that field, matters took a different turn. There was a long series of quiet preliminary inquiries that paved the way for the splendid demonstrations of spectrum analysis, but which were unappreciated and thrown into the shade after that brilliant discovery. A new epoch seemed to be suddenly created, and men cared little to know who had gone before and prepared for it. Unfortunately, this condition of things was favorable to the misappropriation of results gained by pioneer laborers. As the conductors of the "Philosophical Magazine" were of course aware of what had appeared in their pages, and were familiar with the early history of this train of researches, we had not much doubt that they would speak to the point when the time came. Our readers will observe that in the subjoined notice of Dr. Draper's work they have done so, thus decisively confirming the positions that we have formerly taken in regard to the priority of Dr. Draper in the investigations that led up to spectrum analysis.

Dr. Draper here brings together the scattered memoirs and essays that he has written during the past forty years on subjects connected with radiation and radiant energy. They are thirty in number, and, for the most part, are simply reprints; but in a few cases the original memoirs are condensed, and in one or two cases the article here given is the substance of a considerable number of detached articles. Most of them have already appeared in our pages; the earliest of them, on subjects relating to photography, appeared in 1840. "I have endeavored," the author tells us, "to reproduce these memoirs as they were originally published. When considerations of conciseness have obliged me to be contented with an abstract, it has always been so stated, and the place where the original may be found has been given. Sometimes, the circumstances seeming to call for it, additional matter has been introduced; but this has always been formally indicated under the title of 'Notes,' or included in parentheses" (p. x.).

It is probably known to our readers that Count Rumford made a donation to the American Academy of Arts and Science (similar to that which he made to the Royal Society) for rewarding discoveries and improvements relating to light and heat made in America. The Academy has been rather chary of bestowing its honors, and had only awarded its Rumford Medal four times before it made the award in 1875 to Dr. J. W. Draper "for his researches in radiant energy." This circumstance has determined the selection of articles in the present volume. It comprises the researches on which the award was founded.

The President's statement of the grounds of the award is given in the Appendix, and may be summarized as follows:

(a.) Independent discovery of Moser's images.

(b.) Measurement of the intensity of chemical action of light, by exposing to the source of light a mixture of equal volumes of chlorine and hydrogen.

(c.) Application of Daguerreotype process to taking portraits.

(d.) Application of ruled glasses and specula to produce spectra for the study of the chemical action of light.

(e.) Investigation of the nature of the rays absorbed by growing plants in sunlight.

(f.) Discussion of the chemical action of light, and proof that rays of all wavelengths are capable of producing chemical changes.

(g.) Researches on the distribution of heat in the spectrum.

And, finally, an elaborate investigation, published in 1847, by which he established the following facts, which we will give in the words of the award:

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° Fahr.

3. The spectrum of an incandescent solid is continuous; it contains neither bright nor dark fixed lines.

4. From common temperatures, nearly up to 977° Fahr., 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,