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January 13, 1923] 
NATURE 
63 

Exhibition of Physical Apparatus. 
IMES have changed since Lord Bacon had to 
complain that ‘‘ the mechanic, little solicitous 
about the investigation of truth, neither directs his 
attention nor applies his hand to anything that is 
not of service to his business.”” The modern “ inter- 
preter of Nature ’’ would contribute scantily to the 
advancement of learning were he bereft of the 
mechanic’s services, and it is by a happy thought, 
therefore, that the Physical and Optical Societies 
bring together every year the manufacturers and users 
of scientific instruments. At their thirteenth annual 
exhibition, held at the Imperial College of Science on 
January 3 and 4, such a wealth of beautiful, and in 
many cases novel, apparatus was to be seen that we 
can only refer to a few of the rie agg interesting 
exhibits, selected somewhat arbitrarily. 
Of special interest to engineers was a micro-indicator 
(Cambridge and Paul, Ltd.) for high-speed engines, 
in which the dimensions of the parts eliminate inertia- 
errors. A specially designed stylus cuts on celluloid 
a minute indicator-diagram which can be enlarged 
ay or examined at once with a micro- 
205 9 he Elverson oscilloscope (Herbert Kennedy 
and Co.) by intermittent illumination made a machine 
at 1500 revolutions appear to be either stationary 
or working at 150 revolutions, enabling faulty action 
to be detected and located. A fine adjustment for : 
derived from a phonic motor was shown in a 
strobometer (Tinsley and Co.), and comprises a friction 
gear providing an infinitely variable speed. A 
tapered drum driven from the phonic motor engages 
an axially movable friction wheel which carries con- 
tacts controlling the intermittent illumination of a 
stroboscopic disc or the like, the position of the wheel 
indicating the frequency of the illumination as a 
percentage of that of the tuning fork which governs 
the phonic motor. 
uch interest was ene in the new celluloid 
mirrors (Adam Hilger, Ltd.), the thickness of which 
is equal to a few wave-lengths of light. These were 
applied to vertical illumination in a microscope (an 
arc lamp failing to heat the celluloid on account of 
its thinness), to acoustic purposes in an optical 
sonometer, and to the transposition of colour com- 
binations in patterns in the chromoscope (The 
Chromoscope Co.). In the latter apparatus each 
element of the design is prepared as a stencil for use 
in conjunction with a Wratten colour screen which 
can be changed at will, and by means of an optical 
device the various elements are viewed in super- 
by transmitted light. Other novelties by 
ilger were an interferometer attachment for calibrat- 
ing microscope racks, indicating backlash, and check- 
ing the fit of the slide ; and some ultra-violet spectro- 
grams on the new Schumann plates which, with a 
_ minimum of gelatine and a fluorescent component in 
their emulsion, require a remarkably short exposure. 
The latest “ Demonstrator’s Lantern '’ (Newton and 
-) could be arranged at will for projecting ordinary 
ides, for opaque objects, for vertical projection, or for 
microscopic, polariscopic, or Oo esi projection. 
Among microscope improvements might be noted a 
Stand and sub-stage (R. and J. Beck, Ltd.) designed 
to prevent mechanical disturbances from causing the 
disappearance of objects from the field of view under 
high power. The enhanced resolving power obtained 
_ by the use of crossed Nicols was demonstrated with 
this instrument. A new saccharimeter (Bellingham 
and Stanley) exhibited several novel features. The 
po ing prism is constructed without the use of 
cement, the visible edge of the half-prism is a natural 
edge of the crystal, and the quartz plate, compounded 
NO. 2776, VOL. 111] 
of right- and left-handed quartz wedges, is within the 
size limit for which flawless crystals are obtainable. 
An annual feature of the exhibition is the display of 
radium apparatus for medical and demonstration 
purposes by Mr. Harrison Glew. Every year it is a 
Cee to see this pioneer, to whom suffering 
humanity owes no small debt. A radiological ion- 
ometer (Watson and Sons) comprised an ionisation 
chamber connected to an electroscope and arranged 
for measuring the precise X-ray dosage administered 
to a patient. Another medical instrument was that 
for estimating the carbon dioxide content of alveolar 
air (Cambridge and Paul). It employs a Shakespear 
katharometer, the thermal] conductivity of a breath 
sample being compared electrically with»that of-pure 
moist air. The smoke nuisance received attention 
in Dr. E. A. Owen's automatic air filter and his 
jet apparatus (Casella and Co.). In the former, 
samples of air are strained through white filter paper 
at regular intervals, the dust content being estimated 
from the colour of the resulting deposit. In the jet 
apparatus, a jet of moist air impinging normally on 
a glass slip is found to deposit its dust, which can 
then be examined microscopically. 
Of electrical testing apparatus there was an im- 
mense variety, from the high-frequency low-voltage 
Moullin voltmeter (Cambridge and Paul), which em- 
ploys a triode valve so arranged as to preclude 
disturbance of the circuits to be measured, to the 
““Meg’”’ insulation tester (Evershed and Vignoles, 
Ltd.), a remarkably light and cheap megger running 
to 10,000 mgo. which should prove a boon to line- 
men. A multiversal test set by Elliott Brothers 
claimed to measure milliamperes, kilovolts, capacities 
and much else, besides functioning in Varley and 
Murray loop tests. A novel relay for radio signals 
was that designed by Mr. Anson (Tinsley and Co.), 
in which a neon lamp in the anode circuit of a triode 
valve intensifies current variations on account of its 
negative characteristic. 
Demonstrations of actual manufacturing processes 
were given by the Igranic Electric Co. (automatic 
winding of transformers) and Dallmeyer, Ltd. (lens- 
making shown by Prag ln ge ; and examples of 
the daily work of the National Physical Laboratory 
aroused much interest. Each day Mr. W. Gamble 
lectured on the ‘‘ Reproduction of Colour by Photo- 
graphic Processes,’’ an outstanding feature of his 
lecture being the projection of slides made by the 
new Eurochrome process, recently acquired from 
Germany by the Austrian State Printing Office. The 
results of this process, the nature of which is some- 
what obscure, mark a substantial advance in the art. 
Prof. E. G. Coker lectured on ‘‘ Recent Photo-Elastic 
Researches on Engineering Problems,’’ giving a beau- 
tiful demonstration of his method, in which the 
distribution of stress in transparent models is traced 
by means of polarised light. In this way he showed 
the effect of shape on stress-distribution in chain 
links, tensile and compressional test specimens, and 
gear and worm wheels in action. He also demon- 
strated the stresses set up during turning, planing, 
and milling, showing that the cutting edge is preceded 
by a region of compression and followed by one of 
tension, the shaving itself being free from stress in 
the neighbourhood of its point of attachment. With 
a burred edge the stresses were seen to oscillate. 
Mr. F, E, Smith, who made the necessary arrange- 
ments, is much to be congratulated on the success 
of the exhibition which failed to furnish any experi- 
mental evidence for the unluckiness of its number. 
Some fifty-six exhibitors participated. C. W. H. 
