Notices respecting New Booh. 391 



slowly. It was interesting to remark during this experiment 

 the gradual decline of the galvanometer needle, until the earth 

 was perfectly dry, when it ceased to indicate any passing cur- 

 rent. The earth was now made wet around, and in contact 

 with the plates, leaving a portion of the earth between them 

 dry. Under these conditions there was no current; but when- 

 ever the earth was all moistened between the plates, the cur- 

 rent of electricity became as strong as at first. A common 

 Wollaston's battery, charged with acid, having the two termi- 

 nals or poles connected by the earth in the vessel, gave similar 

 results; when the earth was dry there was no conduction; 

 when wet, the current passed through easily. All these led to 

 one conclusion, that the conducting medium was the water, 

 which, if I mistake not, had been pointed out some time pre- 

 vious to my experiments, both by Mr. Hunt and Mr. Fox. 

 And they are also the conclusions which Professor Matteucci 

 has more recently come to. 

 Glasgow, 17th October, 1850. 



LI I. Notices respecting New Books. 



On the Strength of Materials ; containing various original and useful 

 Formulae, specially adapted to Tubular Bridges, Wrought Iron and 

 Cast Iron Beams, fyc. By Thomas Tate, Author of the Principles 

 of the Differential Calculus, Factorial Analysis, fyc. London : 

 Longmans, 1850. 



THIS work contains in ninety-six octavo pages the usual formulae, 

 besides those stated to be new, for computing the relative 

 strength of beams of various forms. The notation appears to be 

 well chosen, and the formulae are neat, perspicuous, and convenient 

 for use. Special attention has been given to the subject of hollow 

 beams and tubular bridges ; and the advantages of the cellular struc- 

 ture, angle irons, and other contrivances adopted in the great engi- 

 neering works of the kind recently constructed, are duly set forth 

 and explained. The book, we think, cannot fail to be appreciated 

 by the practical engineer ; though a few tables showing the strength 

 of the materials principally used in construction, and a somewhat 

 greater variety of numerical examples, might possibly have rendered 

 it more generally useful. 



