78 Mr, six’s Account of 
ferent method; and though, in home refpecls, and for home 
purpofes, it may not be io proper as that already defcnbed, vet, 
for home others, it may be found ufeful, and therefore I fhali 
briefly defcribe it. The glafs of this inftrument is in all refpe&s 
the fame as in the former, excepting that the diameters of the 
tubes are fomething larger. It is likewife filled with fpirits of 
wine and mercury, in the fame manner; but the indexes are 
different, being only a fmali tube of black glafs, about 'five- 
fevenths of an inch in length, hermetically fealed at each end, 
containing a piece of fteel wire. An index of this fort is 
placed in the thermometer on either fide, which, having no 
fpring to fupport them, fink down in the fpirits, and reft upon 
the mercury. Whenever the mercury defcends, the index will 
follow it ; but when it rifes, the index will not rife with it, 
and by remaining at the place to which the mercury had de- 
fended, will (hew the greateft degree of heat or cold which 
had happened. In this manner do thefe indexes an five r the 
fame purpofe, though they move direftly contrary to the others 
in the other thermometer ; but this inftrument is not fo eaAly 
rectified as the former, for the moft powerful magnet will not 
bring the index up again while the mercury above prefles 
again ft them ; and although it is poAible to remove the mer- 
cury, and by that means fet the index at liberty, yet inconve- 
niences will be incurred from which the other is entirely free. 
In fome cafes it may be found expedient, inftead of the clou* 
ble thermometer firft deferibed, to make two Angle ones ; one 
to fhew the greateft degree of heat only, and the other the 
cold, each having its proper index (fee Ag. 4. and 5.). The 
Arft has the fmali tube bent down on the left fide, and the 
lower end immerfed in a bulb or Imall ciftern ot mercury, to 
which the external air has free accefs ; the other has the fmali 
tube 
