On Zinc Roofing, 



315 



The power may be increased almost infinitely, by increasing the 

 size of the temporary magnets, by increasing the number and the 

 length of the bars of the permanent magnets, by increasing the width 

 and length of the metallic ribbons surrounding the temporary mag- 

 nets, and with these by increasing the power of the galvanic battery. 



Art. XII. — On Zinc Roofing; by Prof. L. D. Gale, of the New 



York University. 



Read before the Mechanics'- Institute, June 6, 1837. 



TO THE EDITOR. 



Sir- — The following remarks are intended as a reply to a paper by 

 my friend Prof. Caswell, of Brown University, and which appeared 

 in the 31st volume of this Journal. In March, 1836, I published in 

 the Mechanics' Magazine of this city, (New York,) some remarks on 

 zinc as a roofing material, substituted for slate, copper, tin or tiles, 

 in which I stated the bad results that had followed the experiments 

 made on zinc in this city, and pointed out the defects of that metal. 

 Parts of that paper were copied into the newspapers of the day, from 

 which I suppose Prof. C. obtained his idea of its correctness, inas- 

 much as he has both misconceived and misquoted my paper. In 

 the present remarks I shall first state the positions taken in my for- 



