190 Miscellanies. 



endeavored to ascertain the cause of such result. He observed, to 

 his surprise, that in five different cases, vi^ith various plates, the ef- 

 fects in all those which had the relation of 3 to 4, vpere equal. Al- 

 most despairing of being able to discover the cause of this, he hap- 

 pily remarked, that if from a square of 4 inches one square inch be 

 taken off, a surface remains, which has precisely the same perime- 

 ter as the entire square^ He remarked also, that a rectangle of 3 

 inches base by 1 in height has a perimeter equal to a square of 4 

 inches, and also that a rectangle of 6 inches by 2 has the same per- 

 imeter as a square of 4 inches in the side. 



From this he drew the conclusion that zinc plates act in the ratio 

 of their perimeters, and hence that the smallest plates have the great- 

 est relative effect, because they have the greatest relative perimeters. 



A plate of zinc of 4 sq. inches produced an effect represented by 

 the number 9*26. For this plate was substituted another of the 

 same zinc, having 16 inches base and 3 lines in width ; and by this 

 simple modification a force was obtained of 17*18. 



A rectangular plate of zinc of 45 square inches gave 37*50. From 

 this plate there was then cut out one half the surface, leaving a hol- 

 low square equal to the other half. This last gave a force of 35* 10. 



From out of a plate containing 94 sq. inches, a hollow square was 

 cut 3 fines wide, 15i long, and 6 high, having a total surface of lOi 

 sq. inches ; this gave 32*25. The rest of the plate, equivalent to 

 83| sq. inches, (8 times the surface,) gave only 43*50. A plate of 

 94 inches gave 46*20. From the interior of this, 55 inches (that is, 

 8 inches more than half) were removed, and the remaining hollow 

 square gave 41*75. 



These results fully demonstrate the great influence of contour in 

 experiments of this nature. 



Various experiments were made with zinc wire, with a view of in- 

 creasing the effect, both by wrapping the wire round wooden frames, 

 or placing it in a zig zag form, in copper cases, on Dr. WoUaston's 

 plan. The results were very interesting, particularly in relation to 

 the electro-negative metal. 



An electro-motor constructed in this manner is extremely conven- 

 ient and economical, since with a simple wire of zinc all the experi- 

 ments of Ampere relative to electro-dynamic properties may be per- 

 formed. To determine more fully the relation between perimeter 

 and surface, hollow squares or frames of zinc were formed and cov- 

 ered (first) entirely with an isolating substance, viz. black pitch, melt- 



