TRANSACTIONS OF THE SECTIONS. 55 



On the apparent Mechanical Action accompanying Electrical Transfer. 

 By Mrs. Crosse. 



Dr. Playfair stated, that at the last meethig of the Association, Mr. Crosse, who is 

 recently dead, had read a communication on some phsenomena which took place in 

 the electric current, and it was objected on that occasion, that it was possible the gold 

 which was carried over might have been impure gold ; and that it was owing to a 

 solution of copper that was in the gold that these mechanical phaenomena ensued. 

 Mrs. Crosse, with a desire to show the accuracy of her husband's experiments, had 

 since his death repeated the experiment with pure gold, and obtained the results men- 

 tioned in the communication. 



Extracts from a Letter from the Rev. A. S. Farrar, of Queen's College, 

 Oxford, on the late Eruption of Vesuvius {read by Dr. Daubeny). 



The writer sketched the recent history of the volcano down to the late eruption. 

 A new crater was formed in December 1 854 by the sudden giving way of a portion 

 of the summit of the great cone, which, however, revealed little of the internal 

 structure of the mountain, though it discharged only gas. The eruption commenced 

 on May 1st, 1855, from ten craters which broke out in one long line down the north 

 side of the cone. The lava continued to flow for twenty-eight days, and destroyed 

 much valuable property, passing down the ravines between the Monte Somma and 

 the Observatory, and pursuing its course in the plain to a distance of six miles. 

 Professor Palmieri has taken meteorological observations at the Observatory near the 

 Hermitage. The magnets were affected for two days previously to the outburst of the 

 lava, with remarkable oscillations analogous to those observed in 1851, during the 

 earthquake at Melfi. The development of electricity was strongly marked, of a 

 nature always positive, and yielding ditferent results when studied with a fixed con- 

 ductor, and the same made moveable according to Peltier's method. The Neapolitan 

 Professors Scacchi and Palmieri intend to publish their observations. Mr. Farrar 

 concluded with an account of M. Deville's Chemical Observations on the gases 

 emitted by the fumaroles, as recorded in the ' Comptes Reudus ' for June and July, 

 1855. 



On an Indirect Method of ascertaining the presence of Phosphoric Acid in 

 Rochs, where the quantity of that ingredient was too minute to be determi- 

 nable by direct analysis. By Professor Daubeny, M,D., F.R.S. 



The method employed was to sow on a portion of the rock, well-pulverized, and 

 brought into a condition, mechanically speaking, suitable to the growth of a plant, a 

 certain number of seeds in which the amount of phosphoric acid had been deter- 

 mined by a previous analysis. 



It is evident, that whatever excess of phosphoric acid over that existent in the seed 

 was detected in the crop resulting, must be referred to the soil in which the plant 

 had grown, and hence would serve to indicate the existence of that quantity at least 

 in the rock. 



Now when chalk, oolite, magnesian limestone, red sandstone, and other rocks in 

 which organic remains are usually present, were made the subject of experiment, the 

 existence of phosphoric acid in the rock was always detected by the foregoing method, 

 the phosphoric acid in the crop exceeding the amount of that in the seeds sown. 



But when the slates that lie at the bottom of the Silurian system, such as those of 

 Bangor and Llanberris in North Wales, were tested in the same manner, the almost 

 entire absence of phosphoric acid in them was inferred from the scantiness of the 

 crop, which in each instance contained scarcely more of phosphoric acid than had 

 been present in the seeds from which it had been derived. Nor was this owing to 

 any mechanical impediment to their growth ; for when the rock was manured with 

 phosphate of lime, a crop was obtained from it as large as in the preceding cases. 



These experiments tend therefore to show that the rocks above named really were 



