178 



relative intensities and conducting power of several of the metals : 

 but previously to engaging in this inquiry, he made a series of expe- 

 riments, with a view ot determining the law of intensities as depend- 

 ing upon the length and diameter of the wire through which the cur- 

 rent is transmitted. For this purpose it was necessary to devise means 

 of making and breaking the contact in as invariable a manner as pos- 

 sible. This he accomplished by letting the same weight fall from a 

 constant height when the contact was to be broken, and suddenly re- 

 lieving the cylinder of the tension caused by the same weight when 

 the contact was to be formed. He ascertained that portions of wire 

 connected with the one which formed the circuit, but not included in 

 the circuit itself, had scarcely any influence on the intensity of the 

 current. He then enters into various theoretical investigations as to 

 the mode of deducing the absolute intensities of the currents in this 

 mode of experimenting. 



By comparing the intensity of the electricity in wires of one metal 

 with that in wires of each of the others, by means of the arrangement 

 described in the beginning of the paper, and taking a mean of the 

 results, he found the relative intensities in the following metals to be, 

 silver 1520, gold 1 10G, copper 1000, zinc .522, tin 253, platinum 240, 

 iron 223, and lead 124. The author compared these results with 

 those obtained by Davy, Becquerel, Professor Cumming, and Mr. 

 Harris, and states what he considers may have been the causes of the 

 differences. 



The second object of the author's inquiry relates to the law of va- 

 riation of the intensity of the electricity excited in wires of different 

 diameters : for determining which he compares the effects of three 

 different wires of which the diameters were in the proportion of 4, 2, 

 and 1. The results occupy several tables: and the deduction from 

 them, with regard to the law in question, is, that the intensity varies 

 nearly as the square of the diameter : but several causes contribute 

 to interfere with the accuracy of this determination, and to exhibit 

 the power as a mean of 1 *844 instead of 2 ; the principal of which is 

 the action of the coils upon each other. 



By other methods, in which two wires of different lengths and dia- 

 meters are placed so as to oppose each other in their effects, the ac- 

 curacy of the conclusion that this power is the square, was satisfac- 

 torily established. Hence he arrives at the general conclusion, that 

 the intensity or conducting power varies as the mass or weight di- 

 rectly, and as the square of the length inversely. 



A paper was then read, entitled, <e Note on the Tides." By John 

 William Lubbock, Esq. Y.P. and Treasurer of the Royal Society. 



This communication contains some interesting results which Mr. 

 Lubbock has obtained from observations made at Plymouth, Ports- 

 mouth, and Sheerness, under the superintendence of the Masters at- 

 tendant at those dockyards. Mr. Dessiou has, with extraordinary 

 perseverance, just completed the discussion of about 30U0 additional 

 observations of the tides at the London Docks, with a view to found 

 on a more certain basis the corrections of the moon's parallax and 



