

Mr. W. Sturgeon on Electro -Magnetism. 95 



I leave others to determine ; I shall only say that the smallest 

 space which is between 31 atmospheres and 32, on a scale 

 adapted to an eight foot tube, is equal to -~ of an inch — 

 3^ only ; a quantity as great as the nature of the case can 

 possibly require. Mr. Seaward has not informed us how he 

 will make the joint between the glass tube and the metal box, 

 so that it shall remain perfectly tight ; and that under a pres- 

 sure of from one to twenty atmospheres : and I think he will 

 admit that a leakage in this part, however trifling, would be 

 fatal to his plan. 



The difficulty and trouble of ascertaining nicely the capa- 

 cities of the chamber, tube and ball, is no very agreeable em- 

 ployment, particularly when we consider that in using a tube 

 without these incumbrances there is no occasion whatever for 

 measuring capacities. Another very material objection to this 

 complex plan, is the immense trouble of substituting a new 

 tube in case of accidentally breaking the original one; the 

 same difficulties oppose which we meet in adjusting a thermo- 

 meter tube to an old scale. Upon the whole, instead of being 

 " more convenient and correct than the gauge in common use," 

 as its inventor has endeavoured to represent it, I am satisfied 

 that the complexity of this instrument will render it unworthy 

 of our confidence, and, if relied on, will lead to erroneous con- 

 clusions, which the adoption of a simple tube would certainly 

 have avoided. 



Fearing I have trespassed on your pages too much for a 

 subject of this simple description, I am anxious to subscribe 

 myself Yours truly, 



City Road, Feb. 10, 1834. Henry Russell. 



XVIII. Electro-magnet ical Experiments. By Mr. William 

 Sturgeon. 



To the Editors of the Philosophical Magazine and Journal. 

 "DEING desirous to understand the relation that subsists 

 ■*-" between the chemico- and thermo-electric phaenomena, as 

 influenced by the magnet, so as to form a comparison of the 

 widely different apparatus for exhibiting those phaenomena ; 

 and likewise, if possible, to ascertain some general law to be 

 observed in thus comparing the two modes of exciting this in- 

 fluence ; the few following simple experiments suggested them- 

 selves as the most likely to give satisfaction on this point. As 

 this investigation and comparison* seems to have escaped the 



* There may he said to be one objection; for a comparison has cer- 

 tainly been made by a philosopher of acknowledged skill ; and it is with 

 due deference that I cannot subscribe to the conclusions of that gentle- 

 raun - attention 



