414 Mr. H. Tomlinson on certain Sources of Error in 



circuit was broken, and the plates taken out of the liquid. 

 The cathode was found to be covered with a good deposit of 

 copper, but the anode was completely enclosed in a glacial 

 sheath of copper sulphate. 



Another cell, in which the anode had a surface of 4*4 square 

 centimetres, was treated in the same way, and was found to 

 carry a current of one-tenth of an ampere for 14 minutes. 

 The plates were then found to be covered by a similar coating 

 of copper sulphate. 



A similar cell in which the anode had a surface of 7 square 

 centimetres was found to carry one-tenth of an ampere for 

 30 minutes, when the current fell off as before from the same 

 cause. 



Experiments were then made in a similar manner with 

 cells containing a solution the density of which was I'll. 

 When the current density at the anode exceeded one ampere 

 per 20 square centimetres, the plate became covered with 

 black oxide and the current diminished greatly in strength 

 after a few minutes (about 7 minutes for a current-density of 

 one ampere to 7 square centimetres, and 3 minutes for double 

 that current-density). The current does not entirely cease, 

 and will after a few minutes, if the battery be of sufficiently 

 high potential, again assume nearly its former strength. The 

 oxide then falls off and gases are liberated at the surface of 

 the anode, forming a descending stream close to the plate and 

 an ascending stream two or three millimetres further out. 

 As the current-density is diminished, less and less oxidation 

 takes place and it becomes a lighter brown in colour. With 

 a current-density of one ampere to 30 square centimetres the 

 anode became covered with brown oxide, which made the re- 

 sistance of the cell high and variable, but little or no gas was 

 generated. 



No gas was, so far as could be observed, given off at the 

 cathode during any of these experiments. 



XLIX. On certain Sources of Error in Connection with Expe- 

 riments on Torsional Vibrations. By Herbekt Tomlin- 

 son, B.A* 



Introduction. 



DURING a long series of researches on the torsional elas- 

 ticity and internal friction of metals, I have come across 

 certain sources of error in connection with torsional vibrations 



* Communicated by the Physical Society : read June 26, 1886. 



