. Philosophical transactions. ounding atmofphere, would prefs upon the fcale down-ward with the whole force of the difference. If a little morethan half a pint of air was cooled over the fcale to ths heat ofthe ice and glafs containing it, that is, twenty degrees belowthe freezing point, the difference, according to General Roystable, would have been the eighth part of a grain, whichwas the weight acquired ; but the air within half an inch ofthe glafs veffel being only one degree below the freezing pointyI cannot conceive, that even an eighth part of a pint of aircould be cooled over the fcale
. Philosophical transactions. ounding atmofphere, would prefs upon the fcale down-ward with the whole force of the difference. If a little morethan half a pint of air was cooled over the fcale to ths heat ofthe ice and glafs containing it, that is, twenty degrees belowthe freezing point, the difference, according to General Roystable, would have been the eighth part of a grain, whichwas the weight acquired ; but the air within half an inch ofthe glafs veffel being only one degree below the freezing pointyI cannot conceive, that even an eighth part of a pint of aircould be cooled over the fcale to twenty degrees below thefreezing point; nor that the whole difference of the weight ofthe air over the fcale could ever amount to the ^zd of a grain,I have, however, contrived an apparatus which is executing, inwhich this caufe of fallacy will be totally removed. I (hall,therefore, reft at prefent the ftate of this part of the fubject ;and leave it only proved, that water gains weight on beingfiozen. I am. Sec G. FORDYCE,. [ 366 ] XX11. Sketches and Defcriptlons of three Jlmple Injlruments fordrawhig Architediure and Mcichinery hi PeffpeSiive. By Mr*James Peacock; cotmrnmicatedby Robert Myltie, Efq» , Read March 17, 1785. i- OME of the following machines muft be placed upon thefront edge of tlie table upon which they are to fights may befupported by a three-legged ftocks of the fquares or indexes may have fteel fpringsupon their edges, in order to keep them in any affigned part ofthe grooves in which they are to Aide. F I G. I. (t AEi XIII.) ABCD a drawing board, to be fixed on a table or ftand, &c,in a vertical pofition. AB a fliding-piece for the top of the Tfquare, having a rebate therein to form a groove, as expreffedby the dotted line. CD, fliding-piece for the bottom of the fquare,having a rebate therein to form a groove for the reception ofthe ftock as defcribed by the dotted line; this fliding-piece tobe of fufficient length to receive and
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