96 
NATURE 
[JANUARY 20, 1923 

TEMPERATURE - RADIATION. FROM CLoups.— The 
temperature-radiation from clouds at night is dis- 
cussed by A. Defant in Geografiska Annaler (1922 H. f.). 
Some of the radiation that leaves the cloud is absorbed 
during its descent to the measuring instrument, 
which is placed on the ground. At the same time 
the intervening clear air sends out its own temperature- 
radiation, some of which reaches the instrument. 
By making allowance for these complications, Defant 
calculates that a uniform stratus cloud radiates from 
its lower surface with an intensity almost the same 
as (actually 2} per cent. greater than) that of a “‘ full” 
radiator at the temperature of the cloud. His 
calculation involves the assumption that the only 
constituent of the clear atmosphere which radiates 
energy is the water-vapour. He also reduces observa- 
tions of the nocturnal cooling of the air at various 
observatories, and finds that : 
(the cooling per hour (same quantity when sky 
when w tenths of = clear) (1 — 0-76 w/Io). 
sky are clouded) 
WATER POWER IN IND1A.—The issue of the Journal 
of the Royal Society of Arts for December 15 contains 
the report of a meeting at which a paper by Mr. 
J. W. Meares on “ The Development of Water Power 
in India ’’ was read and discussed. The paper was 
largely a condensed account of information collected 
by the Hydro-Electric Survey of India and published 
in extenso in the Triennial Report of last year. Mr. 
Meares, as Electrical Adviser to the Indian Govern- 
ment, was associated, first with the late Mr. G. T 
Barlow, and later with Mr. F. E. Bull, successively 
Chief Engineers of the Survey, in the preparation of 
the report, and in the analysis of data for potential 
hydro-electric development schemes. The salient 
results of the investigation were as follows. In the 
year 1921, some 350,000 e.h.p. had been developed, 
or was in course of realisation. Sites had been 
examined which gave satisfactory evidence of a 
further 14 million e.h.p. continuously throughout 
the year. Other sites, not fully examined, were 
reasonably expected to yield a further 14 million e.h.p. 
continuously. Finally, there were sites of which 
little was known but their existence, the capacity 
» of which was speculatively, but cautiously, reckoned 
at 4 million e.h.p., so that “‘it is perfectly safe to 
say that at least 7 million e.h.p. is in sight on the most 
conservative estimate and on the basis of absolute 
minimum continuous power.” In announcing these 
tesults, Mr. Meares deplored the fact that he was 
practically in the position of delivering a funeral 
oration on the Survey, which was moribund for lack 
of financial assistance. 
An Etecrric Microscope Lamp.—We have 
received from Messrs. Ogilvy and Co., 18 Bloomsbury 
Sq., W.C.1, a new form of electric microscope lamp, 
specially designed for research work. An opal 
electric bulb of the half-watt type is enclosed within 
a cylindrical metal hood which is practically light 
proof, though well ventilated. The holder of the 
electric bulb is provided with a push-bar switch. 
The base of the metal hood is detachable, and a slot 
cut in it fitting over a clamping screw with milled 
head ensures replacement in the correct position. The 
hood runs on an upright pillar supported on a heavy 
tripod base, which gives complete stability, and can 
be clamped by screws with milled heads in any 
position of elevation and inclination. The light 
passes through a circular window cut in the metal 
hood ; this is provided with an iris diaphragm, by 
means of which the size of the source of light may 
be regulated. A small prismatic optical bench is 
attached to the front of the base of the metal hood ; 
this carries two adjustable supports on saddle stands. 
On one of these is a condensing system, provided with 
NO. 2777, VOL. IIT] 
centring screws and iris diaphragm, which is hinged 
so that if required it may be swung out of the optic — 
axis. The other support is a holder for a cell or 
light filters. By these arrangements perfect centra- 
tion of the light and “‘critical’’ illumination are 
obtainable. The instrument is beautifully finished 
and fulfils the purpose claimed for it; the price 
(12l. Ios.) is reasonable, though we fear beyond the 
reach of most microscopists. 
An Arc REcTIFIER.—At the meeting of the French 
Physical Society on June 16, MM. L. Dunoyer and 
P. Toulon gave an account of their experiments 
on the passage of current through an alternating 
electric arc with one of the electrodes cooled by the 
circulation of water through it. They find that 
whatever the material of the cooled electrode the 
current only flows when that electrode is the anode. 
They explain this result as due to the inability of 
the cooled electrode when it is the cathode to emit 
the electrons necessary to carry the current. The 
same effect is obtained between a third cooled 
electrode and either of the two electrodes of an 
ordinary alternating arc into which it is introduced. 
With this arrangement it has been possible from 
an alternating arc at 110 volts taking 2-5 amperes 
to obtain by means of a transformer in circuit applying 
an average of 95 volts to a cooled third electrode 
a rectified current of 90 amperes. The rectified are 
is stable, but the rectified current is not yet steady 
enough for many industrial purposes. 
THE GaumMont LouUD-SPEAKING TELEPHONE.—At 
the meeting of the Paris Academy of Sciences on 
November 27, M. L. Gaumont gave an account of 
his new loud-speaking telephone, and an illustrated 
article on it appears in La Nature for December 16. 
The vibrating part of the instrument consists of a silk 
cone of angle 90° on which is coiled from base to 
summit a fine wire of aluminium, through which 
the telephonic current is sent. The cone is placed 
between cone-shaped poles of an electromagnet and 
its base is attached to one pole by a collar. As the 
vibrating cone possesses no period of its own, its 
motions reproduce without distortion those of the 
membrane which produced the current. These 
motions are communicated to the air around the 
instrument through holes bored in one of the pole 
pieces and through a trumpet-shaped mouthpiece. 
With a silk cone of 5-5 cm. diameter weighing I gram 
it was possible to make an ordinary speaking voice 
heard throughout a room holding 6000 persons 
without any distortion of the sounds. By introduc- 
ing a triode valve in the circuit the apparatus trans- 
mitted the sound 300 metres. 
LARGE THERMIONIC VALVES.—At the Institution 
of Electrical Engineers on December 7 there was an 
interesting exhibition of 10 kilowatt vacuum tubes, 
which are recent developments of the thermionic 
rectifying valve described by Prof. Fleming in 1904. 
The large to k.w. tubes are used for radio trans- 
mission and are of two types, the rectifier (two 
electrodes) and the oscillator or amplifier (three 
electrodes). The tubes have water-cooled anodes 
consisting of a copper tube which is fused to the glass 
bulb by means of a special copper-glass seal. When 
in action the tube is mounted so that the anode is 
surrounded by a metal joint through which cooling 
water circulates. In the 1o k.w. tube the filament 
current is 24 amperes, the filament voltage is 32, 
and the normal plate voltage is 10,000. The power 
taken by the tube, including the losses inside the tube, 
is 15 kilowatts and the output power delivered from 
the tube is 10 kilowatts. The perfecting of these 
large valves will have a great influence on the future 
development of radio-communication. 

