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Proceedings of the Royal Society 
In addition to this substance, which served as a starting-point 
for the research, the nitrate, the chloroplatinate, the chloraurate, 
the bromaurate, and compounds formed by the action of the hydro- 
bromate on the oxides of mercury, copper, and lead, on ammonia 
and on ethylate of sodium were examined. 
Corresponding addition products of sulphide of ethyl were also 
prepared, but owing to the extremely deliquescent character of 
the hydrobromate of ethyl-thetine, attention was chiefly devoted 
to the derivatives of the methyl compound. 
Iodacetic ether does not form an addition product with sulphide 
of methyl. The reaction here takes a different direction, free 
iodine and iodide of trimethylsulphine being produced. The 
authors are engaged in the investigation of this reaction, and also 
of the products of the oxidation of the thetine compounds. 
5. Note on the Various Possible Expressions for the Force 
Exerted by an Element of one Linear Conductor on an 
Element of another. By Professor Tait. 
In the Quarterly Mathematical Journal for 1860, I gave a 
quaternion process for obtaining in a very simple manner, from 
Ampere’s experimental data, his well-known expression for the 
mutual action between two elements of currents. As one of the 
data the assumption was made, after Ampere, that the action is a 
force whose direction is that of the line joining the middle points 
of the elements, i.e ., it was assumed that the necessary equality of 
action and reaction holds, not merely for two closed circuits but, for 
each pair of elements of these circuits. I promised in that paper to 
publish a more general investigation, in which no such assumption 
should be made ; but I was prevented from doing this by having 
seen a reference to a memoir by Cellerier, in which it was stated 
that such an investigation had been given. I did not, till very re- 
cently, succeed in getting any information about that memoir, none 
of which seems indeed to have been printed except a very brief 
extract in the Gomptes Rendus for 1850, vol. xxx., giving no 
details: but the subject was recalled to my memory by Clerk- 
Maxwell’s Treatise on Electricity , &c ., in which there is an investi- 
