TRANSACTIONS OF SECTION A. 447 
number of deaths, marriages, &ce. at every age. These are then added together and 
compared with the observed numbers of deaths, marriages, &c., and the deviations 
are noted. These indicate where our curve requires correction ; for instance, they 
may indicate that for a certain range of ages, the ordinates require to be increased 
5 per cent., and for other ages to be diminished 3 per cent. The corrections thus 
indicated are applied to the curve, and a fresh curve is drawn which will give 
effect to them as far as is possible without introducing irregularities. The ordi- 
nates of this second curve are then read off, and compared as before with the 
original observations, and the process repeated as often as may be found necessary, 
12. On the Action of Currents of Air between Plates. 
By Puixie Brana, F.C.S. 
On investigating the cause of what is known as Faraday’s experiment on the 
aspirating power of currents of air, I contrived an apparatus consisting of two 
metal plates 5 cm. diameter, to one of which a tube 4 mm. diameter is attached, 
and to the other a tube with a hole‘!mm. ‘The plates can be adjusted parallel to 
each other at any required distance, and also the plate with the small hole is 
movable parallel to its plane, the distance between centres of plates being 
measurable. 
A current of air at constant pressure is forced between the plates from the larger 
tube, the smaller tube being connected with a pressure gauge. 
A series of experiments (illustrated by curves submitted) showed that there are 
certain points at which the resultant vacuum area is greater than pressure, and 
others at which pressure is greater, showing that the phenomenon is due to a series 
of yibrations which are further apparent when higher pressure is employed. 
13. A new Reflector for Incandescent Electric Lamps. 
; By Professor Frank Crowes, D.Sc. 
Recent experiments have proved the practicability of a method recently proposed 
for securing complete or partial forward reflexion in any direction of the light 
emitted from the back of the incandescent filament of the lamp. The idea was 
conceived of attaching a metallic film to the exterior of the glass globe, this film 
being applied in any desired part, so as to secure reflexion from any portion of the 
surface, and also, if necessary, in so thina form as to allow a certain amount of light 
to be transmitted, and a portion only reflected. 
The films experimented upon thus far have been silver films deposited from an 
ammoniacal solution of silver tartrate. It has been found easy to produce these of 
any desired opacity by varying the strength of the solution ; they have usually been 
protected from injury by coating them with varnish. Direct photometric measure- 
ment shows that a Swan lamp, after being silvered over half its surface, throws 
forward practically twice as much light as it did before being thus prepared. The 
skeleton-like appearance of the luminous filament is also removed by this method 
of reflexion. 
The preliminary experiments thus far made seem to indicate that this method 
of applying the metallic film is cheap and easy, and there are manifest advantages 
in employing a metal with such high reflecting power as silver. 
There are many applications of the lamp for which the reflector suggests itself ; 
for the writing-table, billiard-table, and frequently for general illumination of rooms 
from wall-brackets, the opaque film seems appropriate, whilst in other cases a par- 
tially transparent film causes the larger part of the light to be thrown forward, 
oe enough light is transmitted to sufficiently illuminate the space behind the 
amp. 
The convenience of having the reflector upon the lamp itself, and therefore 
requiring no separate attachment or support, will be evident. 
