The Specific Gravities of solid Bodies. 259 



understanding, any errors of magnitude are less likely to be 

 made. 



I constructed one of these instruments with a spring capable 

 of sustaining about one pound when it was extended six inches. 

 Another required four to five ounces to stretch it through the 

 like space, and might be loaded with six or seven without 

 injury. A third, with spring made of small harpsichord wire, 

 stretched about six inches with 50 grains, and was extremely 

 sensible. 



The stiffness of these and similar springs depends not only 

 upon the thickness of the wire of which they are made, the 

 diameter, and the number of the coils, but also in a great mea- 

 sure upon the degree of hardness or temper given to the steel 

 or other material used in their manufacture. The following 

 table (1.) shews the jesult of some experiments I made with a 

 variety of springs of steel of the same quality, and equally 

 tempered, or as nearly so as could be effected by tempering the 

 ■whole at one process ; the wire was 0.045 inches diameter. 



Column 1 is the mean diameter of each spring in inches, and 

 column 2 the number of coils of wire when the springs were 

 in their natural state or not stretched; column 3, the space in 

 inches through which the extremity of each spring was extended 

 by a weight of 10,000 grains. 



Table I. 



In Table II, (arranged as the last) the springs were of highly 

 tempered steel ; iu Tables 111. and IV. the springs were of hard 

 iron wire, and sustained the weights given without injury. 



