THE HELIOTYPE PROCESS. 59 



invention of the electric telegraph? Does not the published flora of the 

 United States show that something has been done in botany? Have not 

 very important investigations been made here on the induction of magne- 

 tism in iron, the effect of magnetic currents on one another, the translation 

 of quantity into intensity, and the converse? Was it not here that the 

 radiations of incandescence were first investigated, the connection of in- 

 creasing temperature with increasing refrangibility shown, the distribution 

 of light, heat, and chemical activity in the solar spectrum ascertained, and 

 some of the fundamental facts in spectrum analysis developed long before 

 general attention was given to that subject in Europe? Here the first pho- 

 tograph of the moon was taken, here the first of the diffraction spectrums 

 was produced, here the first portraits of the human face were made — an ex- 

 periment that has given rise to an important industrial art ! 



Of our own special science, chemistry, it may be affirmed that nowhere are 

 its most advanced ideas, its new conceptions, better understood or more 

 eagerly received. But how useless would it be for me to attempt a descrip- 

 tion in these few moments of what Prof, Silliman, in the work to which I 

 have already referred, found that he could not include on more than one 

 hundred closely-printed pages, though he proj)Osed merely to give the 

 names of American chemists and the titles of their works! It would be 

 equally useless and indeed an invidious task to offer a selection; but this 

 may be said, that among the more prominent memoirs there are many not 

 inferior to the foremost that the chemical literature of Europe can present. 

 How unsatisfactory, then, is this brief statement I have made of what might 

 be justly claimed for American science! Had it been ten times as long, 

 and far more forcibly offered, it would still have fallen short of complete- 

 ness. I still should have been open to the accusation of not having done 

 justice to the subject. 



Have those who gloat over the shortcomings of American science ever 

 examined the Coast Survey reports, those of the Naval Observatoiy, the 

 Smithsonian contributions, those of the American Association for the Ad- 

 vancement of Science, the proceedings of the American Academy of Arts 

 and Science, those of the American Philosophical Society, the Lyceum of 

 Natural History, and our leading scientific ^periodicals? Have they ever 

 looked at the numerous reports published by the authority of Congress on 

 geographical, geological, engineering and other subjects — reports often in 

 imposing quartos magnificently illustrated? — Frof. J. W. Draper 'in Popular- 

 Science Monthly. 



THE HELIOTYPE PROCESS. 



The principle on which the heliotype process is based was discovered by 

 M. Poitevin, a Frenchman, more than twenty years ago, but the working 

 of it as described by him was not found to be practicable. Yarious modifi- 

 cations have been suggested from time to time with more or less success. 

 In the heliotype process, beyond the actual principle, every part, step and 

 method, is peculiar to itself, and has been protected by patents in Europe 

 and the United States. 



The principle above referred to is, that gelatine, which ordinarily absorbs 

 water very readily, when treated with a bi-chromate and exposed to the 

 action of light loses this property and becomes water-proof to a greater or 

 less degree, according as the action of the light is greater or less. So that 

 by allowing light to act through a photographic negative on a sheet of bi- 

 chromatized gelatine, we can communicate to the gelatine the same prop- 

 erty Avhich is given to a lithographic stone, by drawing upon it with greasy 



