PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 333 



Mr. E. Stevens was of opinion that insurance companies had no faith in 

 liglitning-roths, as he never knew them to make any deduction in their rates 

 of insurance on houses wliich were supplied with rods. 



The Chairman remarked tliat this greatest invention of Dr. Benjamin 

 Franklin was not designed to draw the lightning from a great distance. 

 Tiie bolt, when discharged, takes its direction, which is changed somewhat 

 by good conductors. A house in its path is saved, if it has upon it a good 

 metallic conductor of electricity, extending into the earth to a point where 

 it is ahvays moist, because the fluid, so called, takes the route which will 

 allow it to reach the earth in the shortest possible time, and thus restore 

 the equilibrium. That portion of a roof which is regarded as absolutely 

 protected is a circle whose radius is equal to the height to which the rod 

 extends above the roof; hence it is a common practice to have several ter- 

 minations or branches of the main rod, projecting from the highest part of 

 the roof and from the corners of the building. 



Mr. Maynard said that houses having metallic roofs, with gutters and 

 leaders I'unning to the ground, when wet, are perfect conductors. 



Mr. Bull inquired whether any one present remembered an instance of a 

 steamboat being struck with lightning. He had never heard of such an 

 occurrence. 



The Chairman said accounts of sailing vessels being struck are not un- 

 common. He was not aware that steamboats have been; but he believed 

 locomotives were not as lucky. Hardware stores, although filled with 

 metal, are seldom, if ever, injured by lightning. The cm-rent does not 

 always descend from the sky to the earth. The earth is generally negative 

 and the clcud positive; but, if the earth was positive and the cloud nega- 

 tive, the direction of the electric force would be reversed. 



Utilization of Waste Products. 



Prof. Joy, of Columbia College, opened the discussion of the subject by 

 saying this vast subject embraces almost every material employed by man. 

 There are more things wasted than used in many departments of manufact- 

 ures. A few of the more remarkable instances where methods have been 

 lately introduced for utilizing the waste materials will be mentioned — 

 first: 



Soup from Brine. 



The brine in which flesh has been preserved contains, according to Leibig, 

 the r^.ost nutritive portion of the meat. The brine containing the extract 

 has usually been thrown away. Mr. Whitelaw of Glascow had applied the 

 action known as Dialysis to the separation of the salt from those contain- 

 ing sustenance. He says when fresh meat has been sprinkled for a few 

 days with salt, it was found swimming in brine. Fresh meat contained 

 more than three-fourths of itft weight of water, M'hich was retained in it as 

 in a sponga. But the fle-sh had not the power to retain the brine to that 

 extent, and in similar circumstances it absorbed only about one-half as 

 much saturated brine as water, so that under the action of salt flesh 

 allowed a portion of its water to flow out. This expelled water as might 

 naturally be expected, was saturated with the soluble ingredients of the 



