430 
NATURE 
[JUNE 27, 1912 
tion to anyone specially interested in this important 
branch of optics. 
Messrs. Adam Hilger showed many of the speciali- 
ties requiring the highest skill of the optician, such 
as Echelon and Lummer Gehreke spectroscopes and 
quartz spectrographs. Among a fine series of survey- 
ing instruments, shown by Messrs. Casella, Negretti 
and Zambra, Ottway, Pillisher, and others, was a 
divided circle shown by Messrs. E. R. Watts and 
Son, the graduations of which have been investigated 
at Charlottenburg for the purpose of checking the 
accuracy of their dividing engine. The result is that 
the average error is not greater than half a second, 
and nowhere reaches two seconds, a notable achieve- 
ment. 
One of the most important commercial develop- 
ments in optics in recent years has been the growing 
use of high-class photographic lenses. ‘The intelligent 
user has discarded the rectilinear, and the production 
of anastigmat lenses of the highest quality has been 
encouraged by the rapid growth of kinematography. 
Anastigmats at very moderate prices were shown by 
Messrs. Aldis, by Messrs. R. and J. Beck, whose 
Isostigmar and Neostigmar series are notable as 
examples of a new and excellent type, by Messrs. 
Dallmeyer, and others. 
In the meteorological section examples of Dines 
anemometers and the Dines-Shaw microbarograph 
were exhibited by Messrs. R. W. Munro and by 
Messrs. Negretti and Zambra, both inventions of the 
greatest importance. 
It is impossible to give little more than the names 
of some of the seventy exhibitors in the most impor- 
tant classes. The fifty pages of the section dealing 
with microscopes contain short accounts of the chief 
products of Messrs. C. Baker, R. and J. Beck, Messrs. 
Pillisher, Reynolds and Branson, and W. Watson. 
Among the exhibitors of spectacles and ophthalmic 
apparatus were the Kryptok and Unibifocal Co., pro- 
ducing bifocal spectacle lenses of two different types, 
both requiring great skill in manufacture, and Messrs. 
G. Culver, Ltd., W. Gowlland, Raphaels, Reiner and 
Keeler, Ltd., and J. and H. Taylor, who had a large 
selection of interesting oculists’ apparatus. 
Beautiful examples of special cameras for process 
work, a type little known to the general user, were 
shown by Messrs Hunters, Ltd., and A. W. Penrose, 
Ltd. Modern types of projection apparatus were 
shown by Messrs. Hughes, Newton, and Reynolds and 
Branson. Among several interesting exhibits of the 
latter were projection apparatus suitable for use with | 
ordinary microscopes, and also inexpensive apparatus 
for the projection of opaque objects, diagrams, &c., 
a type which might be more generally used for educa- 
tional purposes and for the use of speakers at the 
meetings of scientific societies. 
The catalogue committee decided to include in 
the catalogue descriptions of apparatus shown by 
firms unable to participate in the exhibition. 
is, for instance, a very interesting account and illus- 
tration of large telescopes of 24 in. and 26 in. aper- 
ture, for the observatories at Santiago and Johannes- 
burg, at present in course of erection in the factory 
of Sir Howard Grubb. Descriptions and illustrations 
are also given of other special apparatus made by the 
firm for many observatories in different parts of the 
world. To teachers and others the catalogue will be 
of value, and we would especially emphasise again 
the importance of many of the introductions, which 
contain valuable information in many branches of 
optics scarcely procurable from other sources. The 
catalogue is obtainable from the publishers, The Elec- 
trician Co., Salisbury Court, Fleet Street, E.C., for 
ts. 4d. post free. 
NO. 2226, vot. 89] 
There | 
| mense. 
_in the unravelling of the puzzle of the colours of the 
OPTICAL SCIENCE." 
INTRODUCTORY. 
See years have elapsed since the first Optical 
Convention assembled in 1905, under the presi- 
dency of Dr. R. T. Glazebrook. Both that gathering 
and the second one, in which we are now met, witness 
to the efforts which are being made, not less by those 
concerned in the industries than by scientific men, 
to promote the progress of optical science and of 
optical trade. Like all other industries which depend 
on the application of scientific discoveries, the optical 
industry has felt the pressure of the times; and a wide- 
spread sense of need that science and manufacture 
must be associated in an alliance more intimate and 
more active than heretofore has been the moving cause 
of both conventions. 
DEVELOPMENT. 
Seven years is but a brief span in the development 
of an industry, or in the history of any science. It 
may well be. that in the seven years which have fled 
since our first convention we have no obvious great 
discovery to chronicle. But if no optical invention of 
first magnitude, or discovery of fundamental im- 
portance, has been announced, it must not be assumed 
that there have been no advances. Progress there has 
been; progress solid and real, all along the line. No 
branch of physical science can in the present day 
remain stationary. The workers are too numerous; 
the rewards of success, whether in the joy of scientific 
discovery, or in fame, or wealth, are too alluring to 
permit stagnation. Moreover, the increase of know- 
ledge, the mastery of principles over phenomena, the 
conquest of the forces of Nature, are cumulative. 
Every attempt at wider generalisations, even if un- 
successful in itself, provokes new researches, and ex- 
tends the foundations for further advance. To this 
truth the science of optics furnishes no exception. The 
| history of optics is scarred with the battles of rival 
| theories, of which the end is not yet determined. 
It 
may, indeed, almost be taken as axiomatic that in all 
efforts to reach the unknown, to advance human know- 
ledge, it is better to set before one’s self some directive 
hypothesis than to work aimlessly. Every great 
pioneer in physical science has to frame conjectures, 
and to keep them, as it were, in a state of solution 
until either confirmed or disproven. He may even 
have half a dozen rival and mutually destructive hypo- 
theses before him as he works. Truth is not infre- 
quently reached by a process of exhaustion, by honestly 
following clues that ultimately prove false, since when 
they are proved to be false the path to truth has been 
more closely delimited than before. Even positive 
error in theory has been know to lead to new and 
valuable results; as when Euler, arguing from the 
false premiss that the human eye is achromatic, de- 
duced the conclusion that it must therefore be possible 
to construct by optical means a lens that should be 
achromatic. 
Newton anp Huycens. 
The influence of Newton in science has been im- 
His great genius, shown in his ‘‘ Opticks ” 
prismatic spectrum, and in his “ Principia,” in laying 
the foundation once for all of the laws of motion and 
of the doctrine of universal gravitation, won for him 
an almost idolatrous regard. We may recall Alexander 
| Pope’s couplet :— 
“Nature and Nature's laws lay hid in night: 
God said, ‘ Let Newton be,’ and all was light.’ 
Even his mistakes—and they were few—were accepted 
as dogmas, as when he pronounced the dispersive 
1 From the Presidential Address delivered hefore the Optical Convention 
on June 19 by Prof. Silvanus P. Thompson, F.R.S. 
