870 Transactioxs of the American Institute. 



Mr. J. K. Fisher said that a plan of life insurance by railroad 

 companies M'ould tend best to secure greater care for the safety of 

 passengers, and the use of iron cars and iire-proof wood, and the 

 employment of first quality materials generally, would be much 

 better than costly safetj^ appliances. 



Aurora Borealis. 

 Dr. A. W. Hall further explained his theory of the aurora borealis 

 as being due to the reflected light, and Dr. P. H. Yanderweyde 

 defended the electric theory as advanced by Humboldt, Faraday, 

 Arago, Herschel, and the other eminent scientist's, after which the 

 association adjourned for one week. 



October S8, 1869. 



Professor S. D. Tillman, Esq., in the chair; C. E. Em:ery, Esq., Secretary. 

 The Chairman presented the following scientific notes : 



Contraction of Eubbek by Heat. 

 The Paris Les Mondes says that M. Govi, of Turin, has repeated 

 the experiment M^hich proves that stretched caoutchouc will contract 

 when heat is applied ; but he finds that such contraction only takes 

 place within certain limits of temperature ; and that if a greater 

 degree of heat be applied, though not enough to reduce it to a pasty 

 mass, the rubber expands and becomes rapidly longer. This sub- 

 stance, which has in some aspects puzzled philosophers, especially as 

 regards some of its physical properties, has been frequently con- 

 sidered to consist of a kind of solid foam, made up of a large num- 

 ber of vesicles filled with gas. This theory has been proved to be a 

 i:eality, since Payen and others have seen the vesicles under the 

 microscope, while M. Govi has succeeded in expelling a portion of 

 the gas from the vesicles by softening the rubber with oil of turpen- 

 tine, and withdrawing, by means of an air-pump, the ordinary 

 atmospheric pressure. The peculiar constitution of caoutchouc being 

 admitted, it is easily seen that when that material is stretched, the 

 vesicles will lengthen in the direction of the stretching force, and 

 consequently become more narrow in a perpendicular direction to 

 that force, AVhen, under these conditions, the caoutchouc is heated, 

 the gas within the vesicles, while expanding, will have a tendency to 



