774 
Notes . 
[November*, 
Steevens, of Basingstoke. The regulators are the invention of 
Messrs. Siemens and Halske, of Berlin. They each contain 
19 inches of double carbon, which are consumed at the rate of 
3 inches an hour. The lights consequently will burn for a little 
more than six hours without the regulators being interfered with. 
Seven other lights, of which two are placed in the Court Yard, 
one under the portico, one in the Hall, one in the passage leading 
to the Reading Room, and the remaining two in the engine 
house, are worked by two alternate current machines, and the 
regulators are actuated by two coils acting on a differential prin- 
ciple, one of them forming part of the main circuit and tending 
to separate the carbons, the other tending to bring them into 
contact. The position of the carbons depends therefore not upon 
the strength of the current, but upon the relative amount of 
electricity passing through each coil. The carbons burn for 
about five hours, and may be renewed in half a minute. The 
wires supplying the current for these regulators are laid partly 
in the basement of the building, and partly in pipes under the 
ground. The light given out by each of these lamps is equal to 
600 candles, and their steadiness says much for the excellence of 
the principle upon which they are constructed. The powers of 
the light were severely tested by several of the gentlemen present. 
Mr. George Bullen, Keeper of the Printed Books, put it to 
several practical working tests in different parts of the room, and 
found that at the desks which are farthest from the centre there 
was a decided lack of light for those who, like Mr. Bullen, have 
somewhat impaired their sight by incessant literary labour, while 
at the catalogue desks and in the centre of the room, the light 
was much more than sufficient to read even the smallest print. 
The diameter of the Reading Room it will be remembered is 
exaCtly 140 feet, the half of which is 70 feet. As at present 
placed the three outer lamps hang at a distance of about 35 feet 
from the centre, and of course at an equal distance from the wall. 
A moment’s consideration will show that according to this ar- 
rangement the central portion of the room gets an overplus of 
light, while the part near the wall is underlighted. Mr. Bullen 
consequently suggested that the three outer lamps should be 
hung at a distance from the centre of two-thirds of the radius of 
the circle, by which means each third of the line between the 
centre and the circumference would be equally illuminated. By 
moving the outer lamps nearer the wall the outer row of the 
catalogues will be taken out of the deep shadow in which they 
were thrown by the arrangement adopted on Monday. Dr. 
Carter Blake submitted the purity of the light to some very 
searching colour-tests, and found that the most delicate tints 
were as easily distinguishable as in bright daylight. 
In his excellent lecture on “ Electricity as a Motive Power,” 
delivered to the working men at Sheffield during the Meeting of 
the British Association, Prof. W. E. Ayrton demonstrated that a 
