50 



SCIENCE. 



[N. S. Vol. XVII. No. 419. 



used, especially where the units are rela- 

 tively large. An interesting example of 

 this is noted in the sugar refinery of Glaus 

 Spreckles, in Philadelphia, in which there 

 are some 90 Westinghouse engines about 

 the works, many of them being of 75 and 

 100 horse-power each, others are of 5 and 

 10 horse-power only. A similar subdivided 

 power plant involving 42 engines was 

 erected several years ago at the print works 

 of the Dunnell Co., Pawtucket, R. I. 



It was only a comparatively few years 

 ago when several large and economical 

 Corliss engines were replaced at the Bald- 

 win Locomotive Works by a greater num- 

 ber of small, simple expansion engines, 

 which actually required about 15 per cent, 

 more steam per horse-power-hour than the 

 Corliss engines. This loss, however, was 

 only apparent, for by increasing the num- 

 ber of units and locating them at con- 

 venient centers of distribution much of the 

 shafting and belting could be dispensed 

 with and an actual saving was obtained. 

 Later, these simple engines were replaced 

 by a number of compounds, some eighteen 

 being in service; subsequent tests on these 

 showed a saving of 36 per cent, over that 

 obtained by the use of the simple engines. 



More recently, however, the electric 

 motor has superseded the steam-engine for 

 this work, as its economy and convenience 

 over the latter are now thoroughly recog- 

 nized. 



The statistics of American manufactur- 

 ing compiled by Mr. T. C. Martin for the 

 United States Census Office, show that at 

 the time of the last census, in 1900, electric 

 power was less than five per cent, of all 

 that was in use in such plants, or about 

 500,000 horse-power out of a total of 11,- 

 000,000; but, as Mr. Martin states, things 

 are to be judged by tendencies rather than 

 by the status quo, and these electric motor 



figures exhibit an increase of 1,900 per 

 cent, during the decade. 



The introduction of the electric motor in 

 machine shops and factories was at first 

 looked upon with disfavor and was opposed 

 "by many manufacturers, but the innova- 

 tion obtained a foothold, and advantages 

 which were at first unforeseen were found 

 to attend its use, so that now it is being 

 very generally adopted for a wide variety 

 of work. 



A considerable difference of opinion ex- 

 ists as to whether individual motors should 

 be used with each machine, or whether a 

 number of machines should be arranged in 

 a group and driven from a short line shaft. 



There are well-defined conditions to 

 which each system is best adapted, but 

 there are wide limits between which there 

 appears to be no general rule, and we find 

 both methods occupying the same field. 



For isolated machines and for heavy 

 machines that may be in occasional use the 

 individual motor is particularly well 

 adapted, as it consumes power only when 

 in operation. It is, however, necessary 

 that each motor thus connected shall be 

 capable of supplying sufficient power to 

 operate its machine under the heaviest as 

 well as lightest loads. In certain cases, 

 moreover, the load is liable to very great 

 irregularity, as for instance in metal- 

 working planers, in which the resistance 

 ofliered by the machine at the moment of 

 reversal of the platen is far higher than 

 at other times, and may be so great as to 

 endanger the armature of the motor. Un- 

 der these conditions it is necessary to use 

 a motor of much larger capacity than the 

 average load would indicate. 



Fortunately with electric motors the 

 rated capacity is usually less than tlie safe 

 maximum load, which is determined either 

 by the heating of the conductors, tending 

 to break down the insulation, or by ex- 



