520 Notices of Books. [October, 



complete monograph on the moon which has yet appeared. We 

 may read every part with a perfect feeling of confidence in the 

 exactness of the matter, remembering that it is at once the work 

 of a mathematician, an astronomer and practical observer, and 

 of an elegant writer. 



An Introduction to Physical Measurements. With Appendices 



on Absolute Electrical Measurement, &c. By Dr. F. 



Kohlrausch, Professor-in-Ordinary at the Grand Ducal 



Polytechnic School at Darmstadt, and formerly Professor 



of Physics at the University of Gottingen. Translated 



from the second German edition by T. H. Waller, B.A., 



B.Sc, and H. R. Procter, F.C.S. London: J. and A. 



Churchill. 1873. 8vo. 244 pp. 



Someone (we think Quetelet) has remarked that no science has 



made any great progress until weight, measure, and number 



have been introduced into it, in fact, until it has become more or 



less capable of mathematical treatment. We all know how true 



this is : — The determination of the mechanical equivalent of 



heat raised the science to a position which it never before 



occupied among its brethren ; to which result the admirable 



mathematical deductions of Carnot, Fourier, and, later, of Hirn, 



Helmholtz, and Clausius have also conduced. Again, Ohm's 



law, and the various mathematical problems brought to bear 



upon the subject of electricity by Sir W. Thomson, Clerk 



Maxwell, and others, have quite revolutionised that science. As 



an important means to the end indicated above, we welcome the 



book before us with open hands. It will be invaluable in those 



physical laboratories which are happily commencing to appear 



in this country, and which, by the end of the century, will, we 



trust, have become general in all centres of sound learning. 



The author remarks very truly, " that the mere verbal 

 teaching of physical laws is seldom of much use, tending 

 frequently merely to confuse the student, whilst the simple 

 performance of an experiment gives him confidence in himself 

 and in the laws he is investigating." This work on the measure- 

 ment of physical quantities enables the student the more readily 

 to verify the great laws which obtain in the history of matter 

 and of force. 



The introduction treats, in the first place, of " Errors of 

 Observation," and of the influence of error on the final result. 

 And here we meet with advice on a practice which very 

 frequently prevails in the calculation of final results: — "We 

 may here insist upon the fact that it is generally quite in- 

 admissible arbitrarily to exclude from a series of observations 

 some of the number simply because they do not agree with the 

 greater number. The probability of an increased error being 



