Meafurement of a Baft on Hounflow-Heath. 401 
means of thefe, the rods are not only kept more fteady on the 
flands, againft the common aflion of the wind upon the truf- 
fings ; but they likewife ferve as bolds for the vertical and hori- 
zontal brafs clamps, whereby the rods are made fall; to the. 
ftands on one fide or other, and in both modes of application, 
contacts and coincidences ; as will be more fully explained 
hereafter, in defcribing the tops of the ftands. 
Brafs Standard Scale , and method of laying off the lengths cf the 
Beal Rods. 
At the bale of the mftrumeuts of the late ingenious optician 
Mr. James Short, I purchafed a finely divided brafs fcale, of 
the length of 42 inches, with a Vernier’s diyifion of 100 at 
one end, and one of 50 at the other, whereby the 1000th 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 upon 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 ftandard yard from the Tower, that from 
the Exchequer, and alfo the French half- toife, together with 
the duplicate of the laid fcale, font to Paris for the uie or the* 
Royal Academy of Sciences, were both made by Mr. J&na- • 
than Sisson, under Mr. Graham's immediate diredion. 
Now, although there feemed to be every reafon to fuppofe, 
that the fcale at prefen t in my poffeffion, originally, Mr. Gra- 
. Ggg2 ham’s 
