4 Lovering and Bond on Magnetic Observations at Cambridge. 
Newman’s barometers are superior in several respects to all others. 
The graduated scale which measures the height of the mercury is 
made of brass, and slides by means of a tangent screw so that its end, 
which is of ivory, can be made to touch the upper surface of the mer- 
cury in the cistern. This is known to be the case when the reflected 
and actual point are in contact. The tube which holds the mercury 
is 0.512 of an inch in diameter; therefore the effect of capillary attrac- 
tion is inappreciable.* The Royal Society have published in their 
Report a table of corrections for temperature, calculated by Professor 
Schumacher and applicable to this kind of barometers, by which an 
allowance is made for the unequal expansion of the scale and the 
mercury corresponding to every degree from 32° of Fahrenheit 
and for every half inch of the barometer. The vernier of Newman’s 
standard barometer reads off to =4; of an inch. 
The piers which support the transit instrument are situated at B, 
and may be better understood from mo in another part of the 
plate. The piers are 92 feet long, with a tripod base; m is the east 
and west view, and m the north and south view; 0 is a granite ped- 
estal, 6 feet long, 53 feet wide, 2 feet 10 inches deep, firmly rest- 
ing upon a gravel foundation. The lower side of this block of granite 
is 74 feet below the floor. The sides of the transit room are supported 
on independent walls, separated from the base of the transit by a 
trench 3 feet wide which has been filled up with tan to preserve 
the stones from being deranged by frost. Care has been taken not 
to allow the floor to press upon the piers where they enter it. By 
these precautions the instrument is protected from the jar of foot- 
steps in the observatory and the disturbances of carriages. An 
excellent Transit-instrument, made by Troughton and Simms, 4 feet 
long, was placed in adjustment in January, 1840, and a series of 
meridian observations, including moon-culminating stars, has been 
* This correction for a tube whose diameter is 0.5 inch is only 0.003 inch. 
