Notices respecting New Books. 293 



to seventy degrees when this pressure was diminished. In like 

 manner the disengagement of heat varies considerably when 

 the surface of the bases of the rods in contact is either oxidized, 

 polished, or covered with a very thin layer of graphite, oxide 

 of iron, &c. The heat developed is always increased by the 

 oxidation or coating of the surface of the rods with graphite 

 powder. In this case the hottest extremity is always that 

 communicating with the positive pole ; and the most iavour- 

 able case for obtaining the greatest difference of temperature 

 between the positive and negative pole, is that in which the 

 surface of the negative extremity being coated with oxide or 

 grapiiite powder, that of the positive extremity has remained 

 bright. Connecting this fact with that previously mentioned 

 concerning the unequal heating of the two poles, it becomes 

 evident, that since by the transference of matter from the po- 

 sitive to the negative pole the surface of the two poles experi- 

 ences a different alteration, and that the greatest change takes 

 place at the negative pole, the difference of temperature must 

 be due, at least in part, to the difference of alteration of the 

 surface, which is a consequence of the fact of the transference. 

 I hope to have thus shown, experimentally, the connexion 

 which exists between the phaenomena of the voltaic arc ; and 

 I am led to consider them as depending on the transference 

 of matter from the positive to the negative pole. On the other 

 hand, we know from the experiments of MM. Poiret and 

 Becquerel, that the transfer of matter from the positive to the 

 negative pole is a phaenomenon independent of the develop- 

 ment of heat by the electric current. 



XXXVIII. Notices respecting New Books. 



A Treatise on Land Surveying. By John Ainslie. A new and en- 

 larged Edition, embracing Railway, Military, Marine and Geodetical 

 Surveying. By William Galbraith, M.A., F.R.A.S. 



MR. AINSLIE'S book was in the main of a practical character, 

 but it was the work of one who knew his business well. His 

 directions are full and precise, and his examples numerous and in- 

 structive. 



Mr. Galbraith, the editor of the present edition (who is well known 

 for his scientific acquirements and his skill in the use of instruments 

 of the highest class), has not only thoroughly revised Mr. Ainslie's 

 work, but he has added greatly to its value by the composition of an 

 elaborate article on Trigonometrical Surveying and Leveling, which 

 extends to upwards of 200 pages. 



The formulee are given in the most modern form, and their use 



