878 Transactions of the American Institute. 



or of the matter filling space, which trembling, so far as interference 

 o-oes, may be lateral or longitudinal. But the phenomena of the 

 polarization of light show that these vibrations take place transversely 

 to the direction of propagation of the ray. In sound, the vibration 

 is longitudinal ; in heat and light, lateral. Hence, sound-waves may 

 interfere and produce silence, light-waves may interfere and produce 

 darkness, heat-waves may interfere and produce cold. The ear is so 

 constituted that it takes cognizance only of the longitudinal vibrations 

 of the air, though the air vibrates in all directions ; the eye takes 

 notice only of lateral ether vibrations, though the ether vibrates in all 

 directions. Interference was then described and illustrated on the 

 hoard, and the phenomena of fringes shown to result from the over- 

 lapping of waves in unequal phases, which could be a consequence 

 only of undulations. The practical use of such knowledge as this 

 was illustrated by a description of Newton's rings, and the method 

 by means of which these rings may be made to indicate a distance as 

 small as a millionth of an inch. Another instance of the practical 

 application of these facts is Arago's Differential Refractometer, which 

 will show a difference of density in the air of one eight-thousandth 

 part, and by which the refraction of the air has been measured and 

 tables constructed, by whose use-the mariner may find the true alti- 

 tude of the sun. 



The president remarked that the change of pitch of the whistle of 

 a locomotive approaching, passing and receding, is very perceptible. 



Adjourned. 



March 15, 1872. 



Prof. S. D. Tillman in the chair ; Robert Weir, Esq., Secretary. 

 The president read the following notes of scientific progress : 



I. Bessemer's Gun. 

 In the improved plan for heavy ordnance by Mr. Bessemer, the 

 initial pressure is reduced by having a series of smaller charges 

 ignited successively as the shot travels along the bore of the gun. 

 This is, however, the essential feature of the American gun patented 

 by Mr. A. S. Lyman. In order to secure the greatest benefit from 

 this method of applying force, Mr. Bessemer proposes to increase 

 the length of the gun to fifty feet. It is to be made of wrought iron 

 tubes, connected by flanges and strengthened by steel rings. Rota- 

 tion is to be given to an elongated shot, not by rifling the bore of the 



