Q.'t (he Hydromet^. 151 



portion of inflammable air take fire at the elc6lric fhock, and 

 produce thofe luminous and fiery meteors fo aflonifhing to 

 mankind ; while thofe which contain lefs inflammable matter, 

 but a greater quantity of the {'errrt'erous principles, are formed 

 into fire-balls or fi;rruginous ftones of different magnitudes, 

 which defcend on the earth ; whilft the more light, or thoft: 

 which are compoled only of inflanmiable gafes, mount into the 

 upper regions of the atmofphere, where, taking fire, they fly 

 off in luminous vapours. The height to which fome of thefe 

 vapours are carried before thev are decompofed is amazing ; 

 reaching into regions where we fliould imagine the atmofphere 

 would not be of fufticient denfity to fuftain them. But the 

 natural hiflory of the terreftrial atmofphere has iiot yet been 

 fully inveftigated ; nor the power and eftefts of ele6lricity in 

 the formation of litholojiical, mineralogical, vegetable, and 

 animal ful)liances; — fubjeo^ts that demand the attentioii of 

 the moft able chemilts and fagacious philofophers. 

 Dublin, 



XXV. On the Hydrometer. By William Speer, ^fq. 

 Supervijor and Aj[ayer of Spirits in the Port of Dublin* . 



X H E hydrometer, or areometer, as it is called, is an in- 

 ftrument which afcertains the denfity of liqi>ids, weighing 

 unequal malfes with the fame weight. 



This inltrument is of great antiquity, and until lately it 

 was fuppoled to have been invented at the end of tlje fourth 

 century, by Hypatia, the daughter of Theon, the celebrated 

 mathematician of Alexandria : but M. Ufebc Salverte, in a 

 memoir on this i'ubje£l, in the Annales de Cbimie, vol, xxii. 

 has demonllrated its having been invented by Archimedes 

 three hundred years before the period in wliich llvpatja \yas 

 );orn ; and the very elegant Latin defcription he gives of this 

 jnliruinent, frcin an author of great antiquitv, iliows that, 

 in the form, feveral of thole now in ufe djfler but little from 

 lliat ot the original invention. 



1 his inltrument, from the facility and expedition with 

 which it may be applied, has long been in u^e for aiceriain^ 

 ing the Ipeeific gravitv of vr^ious kinds of liquids ; but its 

 application to the |)arlicular purpofc to which it is now ufed 

 is comparatively of niodern date. 



• F.xtraftc.l from his " Knquiry into the Caufts of the F>roii snH Irre- 

 gularities which tdkc plate ill .ilrertaMun^ llic blicn|;c.is ut bpinuious 

 ^i<luors, itc. Loiidun tJto^." 



K 4 Until 



