Meofurement of a Bafe on Hounuo^v-Heath- 401 



means of thefe, the rods are not only kept more ftcady on the 

 {lands, againfi: the common asflion of the wind upon the truf- 

 iings ; hut they Hkewiie ferve as holds for the vertical and hori« 

 zontal hiafs clamps, wherehy the rods are made fafl to the 

 Hands on one Tide or other, and in both modes cf application, 

 contacts and coincidences ; as will be more hilly explained 

 hereafter, in defcribing the tops of the lT:ands. 



Brajs Standard Scale, and method cf laying off the knglhs cf the 



Deal Rods. 



At the fale of the lnil:rnment3 of the late ingenious optician 

 Mr. James Short, I purchaled a hnely divided hrafs Icale, of 

 the length of 42 inches, with a Vernier's divifion of iod at 

 one end, and one of c^o at the other, whereby the loocth part 

 of an inch is very perceptible. It was originally the property 

 of the late Mr. Graham, the celebrated Watch-maker; has 

 the name of Jonathan Sisson engraved npon it ; but is 

 known to have been divided by the late Mr. Bird, who then 

 worked with SissoN. 



It is fufficiently well known to this Society, that their brafs 

 ftandard fcale, about 42 inches long, which contains on it 

 the length of the flandard yard from the Tower, that from 

 the Exchequer, and alfo the French half-toile, together witli 

 the duplicate of the faid fcale, fent to Paris for the ufe of the 

 Royal Academy of Sciences, were both made by Mr. Jona- 

 than Sisson, under Mr. Graham's immediate direction. 

 Now, although there fcemcd to be every reafon to fuppofe, 

 that the fcale at prefent in my poffefiion, originally Mr. Gra-' 



G g g 2 ham's 



