11 



segments are divided into two thicknesses, the inner being per- 

 manently secured to the non-conducting material, and the outer 

 ones, which take all the wear, are fastened to the inner in such 

 a manner that they can be ensily removed when required. 



The commutator brushes, which are composed of strips of 

 hard copper, joined together at the outer ends, are inexpensive 

 and easily renewed. The machines are simple in construction, 

 all the working parts being easily accessible, and the cost of the 

 maintenance low. 



Copy of Report to Prof. John Trowbridge, 



Chairman Committee on Philosophical ^ Mathematical, and other 

 Instruments, at the Fair of Massachusetts Charitable Mechanics 

 Association, Boston, September and October, 1878. 



At 10.30 p. M., on Friday, the 25th of October, 1878, 1 applied 

 the Richard Thompson Indicator to the "Brown" Steam Engine 

 on exhibition, to ascertain the power required to drive the Elec- 

 tric Light on exhibition. I used a pair of instruments which I 

 believe to be correct, one on each end of the cylinder, and, with 

 the assistance of Mr. C. H. Brown, took six pair of diagrams, 

 simultaneously at each test. The diagrams were completed from 

 the reading of Amsler's Polar Planimeter, with the following 

 result, namely: 



Power required to drive one Brush machine, said by them to 

 be equal to four lights — 6.448 horse power; being equal to 1.112 

 horse power for each light. (The No. 5, 12,000 candle Brush 

 machine, giving 4, 5 or 6 lights.) 



Power required to drive one Wallace-Farmer machine, said by 

 them to be equal to three lights, 10.6976 horse power, being 

 equal to 3.5658 horse power for each light. (The 8 inch, 6,000 

 candle machine.) 



Power required to drive one Wallace-Farmer machine, said by 

 them to be equal to five lights, 16.3705 horse power, being equal 

 to 3.274 horse power for each light. (The 9 inch, 10,000 candle 

 machine.) 



