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No. 1684. MECHANICAL EQUIVALENT OF HEAT APPARATUS. Im- 

 proved form. This apparatus consists essentially of one conical surface which 

 fits in another conical surface and when the shaft is rotated the outer conical 

 surface is rotated and with it the inner conical surface is pulled around by fric- 

 tion between the two. This motion may be retarded by placing weights on the 

 weight hanger which is attached to the string running over the pulley. By the 

 proper regulating of the speed and adjusting of the weight, a condition of equili- 

 brium can be obtained. By putting a known amount of water in the conical 

 vessel and measuring its temperature before and after running, the amount of 

 heat generated by the work done in a certain number of revolutions can be 

 found. The mechanical energy used up will be found by the weight times cir- 

 cumference of the pulley times the number of revolutions. This apparatus is 

 therefore capable of measuring in a very definite way the mechanical equivalent 

 of heat. It is very accurately built, mounted on a heavy base, handsomely 

 finished in japanning and nickel plating with speed counter and 50 gram weight 

 hanger and weights of one 500 gram and five 100 gram. The pulley is 25cm. in 

 diameter. The base is about 10 x 20cms. and the height of entire instrument 

 is about 30cms. It is tested and guaranteed and is one of the pieces much used 

 in the many college laboratories ror the accurate determination of this funda- 

 mental quantity. Complete as described. 



This is one of the special pieces described in the text by Prof. Millikan, "Me- 

 chanics, Molecular Physics and Heat. ' ' We manufacture all special pieces of 

 this text and will be glad to send you our list on request. We have lists for 

 practically all of the commonly used texts and can no doubt send a list for your 

 text. Write us giving us the name of your institution and department and the 

 text that you use. Our service will help you in selecting your equipment for 

 the coming year. 



W. M. Welch Scientific Company 



Manufacturers, Importers, and Exporters of Scientific Apparatus 



1516 Orleans Street Chicago, 111^ U. S. A. 



