Page:A Voyage in Space (1913).djvu/65

Note on the Gravity Experiment

The arrangement described on p. 22 is called a "Peaucellier Cell," and can be used to draw a straight line. It was Sir G. H. Darwin who first pointed out that it could be used to illustrate gravity.

Fig. 8.

Notice that (Fig. 8)

${\begin{array}{llcl}&{\mbox{CS}}={\mbox{CM}}+{\mbox{MS}}&=&{\mbox{KM}}+{\mbox{MS}}\\&{\mbox{SK}}&=&{\mbox{KM}}-{\mbox{MS}}\\\therefore &{\mbox{CS}}.{\mbox{SK}}&=&{\mbox{KM}}^{2}-{\mbox{MS}}^{2}\\&&=&{\mbox{KA}}^{2}-{\mbox{AS}}^{2}\end{array}}$

Since KA and AS are a string and a rod of constant