■S7^ HYDROSTATIC BiVLANCE. [Scptcmbqr^ 



tiie lever. Hence^ if C be the place of tlie weight at 

 tlie conclusion of the operation, 



Weight in water : weight in air : : B C : B A. 

 And, by subtraction, the loss of weight in water : 

 w eight ill air : ; A C ; A B ; and hence 

 W-, in air A B 

 — „ equal equal the spec. gray. ; which is 



loss ■ AC ' 



iie rule, ' Q. E. D. 



Substances lighter than water may have, if neces- 

 sary, their specific gravity ascertained by the usu* 

 al method ; a scale of equal parts being cut on the 

 opposite side of the beam, and the article to be weigh*- 

 ed placed in a notch for the purpose. For mineralogy, 

 liov/ever, this will seldom be nece^3sary. The bottom 

 of the notch A (at the smaller end) should be in a line 

 with the edge of the scale, its sides being a little raised. 

 The top of tlie shorter end should be rather the tliick- 

 ast part of it, to allow the horse-hair, by which the mi- 

 neral is suspended, to swing clear. This mode will 

 be found very delicate and accurate, and a hook must 

 not be used, as it cannot be balanced. 



TliC iiistrument, in this form, is exceedingly com 

 pact, and may be reduced to a simple rod. 



The principle is capable of being applied (as iu 

 an iriRtriiment I have made) to an arc of a circle, with 

 a rod resembling in its applicatiou a commou bent Ipt; 

 yer. 



