488 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



ter, the deck and boilers vibrated so as to cause apprehension of damage 

 to the numerous tube-joints of tlic boilers. 



The hour for adjournment having arrived it was resolved to continue the 

 discussion of Iron clad ships at the next meeting. 



The Russian visitors having listened with marked attention to the whole 

 debate withdrew at the close in company with Commodore Porter. 



Adjourned. 



American Institute Polytechnic Association ) 

 October 29, 1863. j 



Chairman, S. D. Tillman, Esq.; Secretary, Mr. J. W. Chambers. 



The miscellaneous business of the evening was opened by the chairman 

 ■with the following remarks : A very interesting meeting of the American 

 photographical society, was held at the N. Y. University on the fifth of 

 this month, at which the results of an important series of experiments 

 were presented in relation to the effect of different colored rays of light on 

 vegetation. These experiments confirmed the investigations of Prof. J. W. 

 Draper made several years before. The most interesting event of the eve- 

 ning was the exhibition of the largest photograph of the moon yet taken. 

 It was made hj Dr. Henry Draper with his new glass reflector. The ad- 

 vantage of using a large reflector instead of a refracting telescope, will 

 be obvious when we consider the diverse qualities of the rays which make 

 up the beam of light arising from the different rates of undulation of the 

 ethereal medium. The red ra}'^ is produced by 458 millions of vibrations 

 in a second ; the violet ray by t27 millions of vibrations. The red ray is 

 the least, and the violet ray the most refrangible ; the yellow or most lumi- 

 nous ray is intermediate; the greatest heating power is in the red ray; the 

 greatest luminosity is in the yellow, and the greatest actinic power is in 

 the violet or beyond it, in what are called the invisible rays. Now it is 

 apparent that these three rays being of different refrangibility, will, on 

 passing through a lens, each have a distinct and separate focus; and that 

 when the lens is fixed so as to present to the eye a perfect image, a sharply 

 defined photographic image could not be taken, at the position of the eye, 

 because the actinic rays, alone performing the chemical action which makes 

 the picture, have net their perfect focus at that point. The larger the lens 

 the greater will be the disparity in the foci. This objection to the lens in 

 ordinary photographic work is not a serious one because the skillful ope- 

 rator can make the requisite allowance to produce a sharp picture; but 

 when a large refractor is used to take distant objects, the diflBculty in ob- 

 taining the proper adjustment becomes greater. The objection does not 

 apply to the reflecting telescope. 



The chairman illustrated upon the blackboard the refrangibility which 

 produces the solar spectrum, and then requested Dr. Rich to read from the 

 N. Y. Evening Post, the following description of 



Draper's Glass Reflector. 

 At a meeting of the New York photographic society, held in the chapel 

 of the university on the evening of Monday, the 11th instant, a large num- 



