Menfurement of a "Bafe on Hon n (low- Heath. 4.^.-^ 



are both reprefented lii the plate, and only differ from 

 each other in the fliape of the brafs milled-headed nuts 

 that work upon the fcrew, of about 2| inches in length, 

 ■ into which the right-hand end of each hook is formed, 

 •Thus, while the nut enters very freely into, and reil:s upon, 

 the fork, the left-hand end of the hook has a circular hole in 

 it, whereby it flips eafdy off and on of the brafs pillar. Bvr 

 referring to the plate, it will appear fufficiently obvious, from 

 the nature of the nut on the left-hand Ir-^ok, that it could onlv 

 move the rod on to coincidence, and could not bring it back 

 again, if the bufniefs happened at any time to be overdone ; 

 in which cafe it was neceffary to move the rod ^ little back- 

 wards by the hand, and then to work anew with the iiXit, 

 until the coincidence was accurate : whereas the nut on the 

 right-hand hook, having two fhoulders, could either pufli or 

 pull the rod forwards or backwards : and although this ap- 

 peared to be an advantage, yet it was found from experience, 

 that it rather bound the hook too much, and occafioned a kind 

 -of fpring in the parts, which fometimes difhurbed the coin- 

 ■cldence on the removal of the hook ; wherefore it was often ap- 

 plied, like the other, by placing the fcrew itfelf in the fork^ 

 and v/orking with both fhoulders of the nut behind it. 



The pofitions of the thermometers, and mahogany oval lid 

 on the top of the cafe, have already been mentionedo This 

 laft, being unlocked and removed, permits the cafe to be looked 

 into, or the hand to be admitted, in order to be certain that 

 the faftenings remain fafe and entire in the infide. Brafs caps, 

 with the refpe£live number of the rods engraved on them, are 

 likewife fcrewed on the maie-fcrews in the ends of the cafe, 

 through which the extremities of the tubes projed, to pre- 

 serve them from accidents when not in ufe. And, laflly, to 



Vol. LXXV. N n n flrengthen 



