OP ARTS AND SCIENCES. 493 



XXIII. 



CONTRIBUTIONS FROM THE PHYSICAL LABORATORY OF THE 

 MASSACHUSETTS INSTITUTE OF TECHNOLOGY. 



XXVIIL — THE EFFICIENCY OF SMALL ELECTRO- 

 MOTORS. 



By H. E. H. Clifford. 



Presented by Charles R. Cross, March 9, 1887. 



The following tests of electro-motors are presented as giving a good 

 exami^Ie of the efficiency of some of the smaller motors in use at the 

 present day. They have been exclusively devoted to the determina- 

 tion of efficiencies, the subjects of governing and of smoothness of 

 running under different loads being left out t^ consideration. The 

 only other series of tests vs^hich has been published in this country, so 

 far as I have been able to learn, is that made on motors and dynamos 

 at the International Electrical Exhibition held at Philadelphia in 1884.* 



The tests have been carried on in the Physical Laboratory of the 

 Massacliusetts Institute of Technology during the years 1885-86, by 

 Messrs. F. A. Pickernell, H. G. Pratt, D. P. Bartlett, and the writer, 

 students at the Institute. 



The number of machines tested was thirteen. I give below their 

 names, together with either a brief description of their peculiarities or 

 a reference to some publication in which they are described. 



Griscom. — S. P. Thompson's Dynamo-Electric Machinery, 2d ed., 

 p. 429. 



Ayrton and Perry. — Ibid., p. 432. 



Gramme " Machine a petite lumiere." — Ibid., p. 120 



Gramme Magneto. — Ibid., p. 117. 



Thompson. — Ibid., 1st ed. p. 354. 



Deprez. — Prescott's Dynamo-Electricity, p. 707. 



Monarch. — An electro-magnet revolving within a ring-shaped elec- 

 tro-magnet making use of consequent poles. The ordinary split-ring 

 commutator is used. 



* Report of Examiners of Section XXIX. Supplement to the Journal of the 

 Franklin Institute, March, 1886. 



