Tallmu Lamp.'^New Metrical S^iflm* 365 



the cup is then eafily filled again by holding up the wire, after which the drops muft be regu- 

 lated again. To lefien this inconvenience as much as poflible, nothing but clean tallow, or 

 hogs' lard, muft be burned. 



Tallow and hogs' lard will burn with a very clear bright flame, of the fame intenfity, tor a 

 long time. 



The fmall cup, when detached from the reft of the apparatus, will fupply the different ufes 

 of a candle: it may be carried about by the tube A, or, occafionally, placed with the tubeyin a 

 fmall wooden ftand. The tallow is not very liable to be fpilled. 



Every time before the lamp is lighted, a new portion of wick muft be drawn through the 

 ring. This is not eafily effected when the tallow is cold ; therefore, to avoid this trouble, 

 it is the beft method always to draw up the wick immediately before the flame is extinguifh- 

 ed ; for which purpofe, fmall forceps, made of one piece of bended iron, will be moft conve- 

 nient. 



Laftly, it may be neceflary to remark, that after the lamp is lighted, when the tallow in 

 both cups is cold, the tallow in the fmall cup muft be broken and ftirred up, that a fufficient 

 quantity may be fufed immediately to fupply the flame ; and the fooner to fufe the tallow in 

 the conical cup, the flame fliould be raifed near to its point, and when there is a ftrong current 

 of air in the room, in that fituation it ought to remain ]f»^ 



XL 



Report made t$ the Injiitute of Sciences and Arts {at Paris), on the 29 Pr arial, in the 

 Seventh Tear Cjune 17, 1799^/, in the Name of the Clafs of Phyjical and Mathematical 

 Sciences, on the Meafure of the Meridian of France, and the Rejults_ which have been dc' 

 duced to determine the new Metrical S^em *. 



(Concluded from p. 324.} 



M. 



LEASURES of furface are eafily deduced from the determination of the length of the 

 metre, which is the bafis of the whole fyftem. But this is not the cafe with meafures of 



• Count Rumford affured me fome time ago, that tallow will burn very well in the common fountain 

 lamp, provided the bafon, or receptacle into which the tallow flows, is fufHciently capacious to hold enough 

 of the material to fupport the combuftion till the tallow in the refervoir is fixed. The principal inconve- 

 nience I found on trying this, was the interception of a large quantity of light by the bafon itfelf, which, 

 neverthelefs, I think may be almoft entirely focceeded, though perhaps not quite as perfeAly as in a candle. 

 Tallow fold retail at the price of candles cofts ten pence a pound, which in the middling-iix will bum above 

 40 hours. Such an illumination will therefore coft Icfs than one fsirthing an hour. I do not know the price, 

 confumption, and quality of oil, but eftiraate it at about half that of tallow* Some better information r«fpc£t- 

 ing both fliall be given in our next number. — N- 



t Abridged from the Journal de Phyfique, FluAldor, An 7. 



Vol. III. — November 1799. 3B weight. 



