PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 923 



expand the same, nearly, at a comiDarativety low temperature, as at 

 a higher heat. Mr. Stephenson, of this city, the omnibus Iniilder, 

 says that it is not necessarj'^ to heat the tires of wheels higher tlian 

 a dull black heat, as they expand no more -at a higher tempera- 

 ture. A boiler twenty feet long will expand three-eighths of an* 

 inch for every 180 degrees. 



Dr. L. Bradley described, at some length, a new method of pre- 

 venting the incrustation of boilers, by electricity, and making the 

 boiler form part of the circuit l)etween the positive and negative 

 pole. This is a western invention, and it is said has been used 

 with decided success on boilers in some of the western states. 



Several gentlemen doubted the efficacy of this arrangement, as 

 it was not clear by what chemical process the incrustation was 

 prevented. It was stated that the plan would be put in practical 

 operation in this city soon, and members would have an opportu- 

 nity of witnessing it. 



The following paper was then read by title : 



Galvanic Batteeies — Quantity and Intensity Currents. 



Dr. L. Bradley. — I do not propose to speak of the elementary 

 principles of the battery, or of the electro-dynamic force generated* 

 by it, but to confine myself to the consideration and promulgation 

 of some of the discoveries I have been able to make, aided by the 

 instruments heretofore descrilied in my paper on the Anthistometer, 

 and to the relative merits of such batteries as are employed in 

 telegraphy. 



Before proceeding further, I will explain what I understand by 

 the words quantity and intensity, as they are commonly used in 

 this branch of science. These words seem to me to be technical, 

 and not to have reference so much to magnitude of any kind, as in 

 the common acceptation of the terms, but to peculiar and distinct 

 properties of currents. 



I define quantity as that property of a current which gives it a 

 great magnetising power, as well as great heating and decompo- 

 sing power. It is the desideratum in all electrolytic pursuits, such 

 as throwing down metals from their salts; in galvanizing, electro- 

 typing, &c., l^ut it is not capable of overcoming any great resist- 

 ance, or of being propagated at any great distance. It is best 

 obtained by large cups, having largo plates, arranged as simple 

 battery, i. e., the positive poles connected, and the negative poles 



