256 Notices of Books. [April, 
with the researches of Faraday in electro-magnetism, and of 
Sir William Thomson in general electric principles. There has 
therefore been much to add, and Dr. Everett is to be congratu- 
lated on his happy method of collating the experiments neces- 
sary to an English work. The description of the various forms 
of electrometers, for instance, leaves nothing to be desired. 
We must again commend the illustrations, and express our 
indebtedness to Messrs. Blackie and Sons for being able to lay 
before our readers a specimen of the exquisite woodcuts. The 
one selected exhibits the image of the carbon points of the 
electric lamp as viewed through a lens, the natural size of the 
carbons being indicated by the sketch at the right hand. The 
book is well bound in limp cloth covers, a style of binding every 
student will appreciate. 
Experimental Mechanics. By Robert STAWELL Batt, A.M, 
Professor of Applied Mathematics and Mechanism in the 
Royal College of Science for Ireland (Science and Art De- 
partment). London and New York: Macmillan and Co. 
1871. 
Turis volume contains the substance of a series of twenty evening 
lectures upon ‘“‘ Experimental Mechanics” delivered by the Author 
at the Royal College of Science for Ireland. The aim has been 
to create in the mind of the student physical ideas corresponding 
to theoretical laws, and thus to produce a work which may be 
regarded either as a supplement or an introduction to manuals of 
theoretical mechanics. We cannot praise the attempt too 
highly, nor congratulate Professor Ball too sincerely upon his 
success. The laws of mechanics are essentially simple, and in 
this work they meet with an appropriate exposition. No com- 
plicated formule are introduced into the calculations, numerical 
or geometrical illustration being chiefly employed. The method 
of treatment of the laws relating to friction, to the mechanical 
powers, to the strength of timber and structures, to the pendu- 
lum and to the laws of motion, is original and extremely explicit. 
But it must not be misunderstood that the work is too simple for 
the advanced student,—far from it. Mr. Ball has well distin- 
guished between the class of students who know mathematics 
and those who do not. Therefore we can safely recommend the 
book to the notice of all. 
