[15J DEFECTIONS FOR COLLECTING ROCKS MERRILL. 



A form of cutting macliine employed for some years in tlie laboratory 

 of the United States Geological Survey, and in favor of whicli much, 

 can be said, consists merely of an endless soft iron wire running like a 

 belt or band saw over two grooved pulleys. These pulleys, which are 

 some 18 inches in diameter, revolve in the same vertical plane. The 

 lower, to which the power is imparted by means of a small pulley and 

 belt, revolves in stationary bearings, while the upper, by means of two 

 upright standards, is free to move a distance of several inches in a 

 vertical direction. This permits the ready replacement of the cutting 

 wire when necessary, while at the same time it permits, by means of 

 weights, a constant tension to be brought upon the wire, otherwise 

 likely to become loose through stretching. At the Survey laboratory 

 a No. 16 soft iron wire is used mainly. After being cut to the right 

 length the ends are beveled and bound with fine wire, such as is used 

 by florists, and then soldered with hard solder. After cooling the 

 excess of solder is removed by filing. The pulleys are made to revolve 

 at about the rate of 400 revolutions per minute, and wet emery applied 

 either by the hand or a brush, while the object to be cut is held imme- 

 diately below. A table, through which the wire runs like a mechanic's 

 band saw, serves to support and steady the object. Such a saw has the 

 advantage of the reciprocating saw above described, in that the pres- 

 sure may be made constant and steady, there being no blow such as is 

 imparted by the constant lifting and dropping of the saw frame in order 

 to allow the cutting material to be washed into the scarf. 



