130 Notices of Books. [January, 
teachers, and he now brings it forward in an extended form in 
the hope that the work may be of service to a larger class of the 
community. 
The first book, consisting of ten chapters, treats of FriCtional 
Electricity, and commences with an account of attraction and 
repulsion, and the dependence of the former on induction. 
Under the head of EleCtrical Machines, the new machines 
of Holtz and Bertscl are described and figured, and the clearest 
account of the former we have ever seen is given here. Con- 
densers and the effeCt of the discharge follow, a short chapter 
on DieleCtrics, a chapter on various sources of electricity besides 
friction, and, finally, a chapter on EleCtrical Measurement. 
In this we find some extremely useful definitions, thus as to 
unit of electricity , the author observes : — “ Each of two equally 
charged bodies is said to have a unit of electricity if, when at a 
distance of one centimetre from one another, the one will repel 
the other with a force which in one second of time would impart 
a velocity of one centimetre a second to one grain of matter.” 
Again, as to that difficult definition the EleCtrical Potential : — 
“ The work which a raised body is capable of doing, if it fell a 
certain [distance, is called the potential work of this body, or 
simply its (mechanical) potential Instead of a unit 
of weight, let us take a unit of electricity The 
eleCtrical potential of a body is the mechanical work which the 
electricity of the body is capable of doing in passing to the earth, 
or other indefinitely great reservoirs of electricity of the same 
kind as the earth’s Potential may be defined as the 
preparedness to do work.” The chapter concludes with an 
account of Thomson’s Electrometer. 
The second book treats of Voltaic EleCtricity, and consists of 
twelve chapters, among which may be specially noted those on 
Measurement, on Resistance Conductivity, EleCtro-Motive 
Force and their Measurement, and on the Relation of EleCtricity 
to Life. In the latter, we are told, in insectivorous and sensitive 
plants a current is established at the moment when the leaf is 
irritated, and when consequently it moves. Again, although 
there seems to be a somewhat intimate connection between 
nervous and eleCtrical excitement, the strongest coil-current 
applied to the head as a cap does not appear to affeCt the think- 
ing faculties. Neither does the aCt of thinking appear to produce 
a current. The third and final book relates to Magnetism, and 
this is followed by two appendices containing useful experi- 
mental hints. 
Dr, Guthrie’s book, without being a popular treatise in the 
broadest sense of the term, combines facile expression, and an 
absence of abstruse treatment, with an account of the more 
recent mathematical development of the science. It is essentially 
a student’s manual : thorough and precise, without being over- 
loaded with dry details and technicalities. The experimental 
