4-68 Notices respecting New Books: — Prof. Fai*aday's 



his chair, in consequence of infirm health, and the present work is 

 the fruit of his leisure, indicating however that, while the powers of 

 his body have been enfeebled, the powers of his mind remain unim- 

 paired. It contains many new, curious, and elegant properties of 

 triangles, quadrilaterals, and conic sections. It abounds also with 

 practical applications, particularly to surveying on an extensive 

 scale. One of the most useful problems in sur\^eying is, given three 

 points in a country, and the angles which the distances between them 

 stibtend at a fourth, to find the distances of these three from the fourth. 

 It is a problem as old as the days of Hipparchus, was applied by 

 Suellius in measuring a degree of the meridian, and has engaged the 

 attention of distinguished analysts in more recent times. This 

 problem Mr. Wallace has solved in a manner extremely convenient 

 for the appUcation of logarithms. Another problem to which Mr. 

 Wallace has paid great attention in this work, may be enunciated as 

 follows : four points in a country being supposed to be joined by straight 

 lines, given the angles of tico of the triangles having one of the six 

 straight lines for a common base, and given also one of the six lines, 

 to find all the other lines and angles in the figure. 



He has shown the success of his formulae by application to ex- 

 amples taken from the great trigonometrical surveys of Britain and 

 France. 



The value of Mr. Wallace's work to surveyors is greatly increased 

 by a particular description of an instrument which he invented some 

 years ago, and which he calls an Eidograph. The object of it is to 

 reduce or enlarge plans in a given ratio. This it accomplishes in a 

 manner far superior to the pantograph, the only instrument pre- 

 viously known for that purpose. Mr. Wallace described the eido- 

 graph in the 13th vol. of the Transactions of the Royal Society of 

 Edinburgh. But it may be hoped that the present work will make 

 this valuable contribution to the arts more extensively known. He 

 has also given a description of some other instruments which he has 

 invented for the solution, by geometrical construction, of the first of 

 the two problems mentioned above. 



Mr. Wallace's work assumes particular imi^ortance at the present 

 moment, when the trigonometrical survey of Britain, which had 

 been suspended for several years, is about to be resumed. We hope 

 that the author's health \\ill continue such for many years as to 

 enable him to enlighten the public by his ingenious labours. 



The Eidograph is made by Mr. Adie, optician, Edinburgh. Price 

 nine guineas. 



Experimental Researches in Electricity. By Michael Faraday, 

 D.C.L., F.R.S., Fullerian Professor of Chemistry in the Royal 

 Institution, &c. Reprinted from the Philosophical Transactions 

 of 1831-18.38. Lond. 1839. 8vo. Pp. 574, with Eight Quarto 

 Plates, 

 It is unnecessary, in addressing the readers of the Philosophical 

 Magazine, either in that particular character, or as members of the 



