( 537 ) 
faid cylindrical Veffel, whofe Diameter on the Infide 
ought to be equal to that of the Terrella, and its 
Depth not lefs than the Radius. Or, if the Terrella 
is truly globular, inftead of the cylindrical there may 
be a concave Vehel (reprefented by the pricked Line 
X n ‘w;) lefs than a Hemifphere, and its Diameter of 
Concavity fomewhat lefs than that of the Terrella ; 
fo (Viall their Contad: be wholly at the Brim of the 
Velfel, which will keep the Terrella central. And 
this may be better than a Cylinder, becaufe lighter, and 
the moft of its Parts nearer to the Axis of its Verti- 
city. Either of thefe is to be centrally fixed to the 
Arbor n which, together with its Pivot f, (hould 
be made of Brafs, and the Pivot Work in a Hole made 
fit for itinaHorfe’s Tooth, orfome fuch Thing : The 
End of the Pivot fhould reft on the Bottom of the Hole, 
that it may move the eafier. The Collar at P, in which 
the Arbor turns round, may be made of Tooth alfo, 
and both that and the Pivot aforefaid {hould be kept 
well oiled, or greafed, to prevent their being heated by 
fo rapid a Motion as is necelfary, and fo ihould alfo the 
other Axles. This is to be kept in Motion by a Gut- 
ftring (as the Spill of a Spinning*Turn is moved) tied 
pretty ftrait round the little Wheel at and the great- 
er one at F, which String is reprefented by the pricked 
Line. And the Wheel F is turned after the fame 
Manner, by a larger Gut- firing round the Wheels #^ 
and(l, which muft be ftrained very ftraight, that it 
may not Aide on the Wheels. To prevent which Incon- 
venience, this String (and the other, if need be) may be 
rubbed well with powdered Rofin. I think a GuN 
firing round a great Wheel and lelfer one, will work 
eafier than the beftof Clock-work, and without rattling 
Z z X or 
