10 
POPULAR SCIENCE N'EWS. 
[January, 1S90. 
colorless and transparent, but often occurs 
beautifully colored in various tints. What- 
ever its own color may be, when a ray of 
light is transmitted through it, the crystal 
appears to become partially self-luminous, 
shining with a faint bluish light, very hard 
to accurately describe in words, but easily 
recognized after being once seen. This phe- 
nomenon, which is by no means confined to 
fluor-spar, is known as fluorescence. 
Fluorescence is due to the property pos- 
sessed b}' many bodies of changing and 
increasing the length of certain waves of 
light, so as to render them visible to the eye. 
The solar spectrum, as is well known, is 
formed by the decomposition of white light 
into its component parts, of different colors 
and wave-lengths. Commencing with the 
red rays, which have the longest wave- 
lengths, and passing along to the violet, the 
wave-lengths continually decrease, until they 
fail to produce the sensation of light upon the 
eye, and are transformed into actinic or 
chemical rays. But the ether-waves still 
exist, although invisible, and, in passing 
through any fluorescent substance, they are 
so lengthened as to be transformed into light, 
and cause the peculiar illumination. There 
are also ether-waves at the opposite, or red, 
end of the spectrum, which are too long to 
produce the sensation of light, and appear as 
heat, but there is no fluorescent substance 
which will shorten them into visibility. The 
action of such substances is always in the 
direction of lengthening the waves. 
Sulphate of quinine is a beautifully fluor- 
escent body. If a solution of this salt is 
placed in the sunshine, it will glow with a 
bluish tint, and if a convex lens is placed 
between the solution and the light, the path 
of the converging rays in the solution is very 
plainly shown. This experiment forms a 
most excellent demonstration of the laws 
governing the action of such lenses upon 
light. 
Characters may be painted upon a screen 
with a solution of sulphate of quinine, or any 
fluorescent substance, and will be quite invis- 
ible by ordinary light, but if the ultra-violet 
rays of the spectrum are allowed to fall upon 
them, they become visible at once. Owing 
to the great actinic power of these ra\s, a 
photograph of such a screen will show these 
invisible characters upon the finished plate. 
Certain mysterious "spirit photographs" 
have been produced in this way. 
Among other notably fluorescent sub- 
stances are iBsculine, a substance extracted 
from the horse-chestnut ; madder, chloro- 
phyll, common kerosene oil, and quite a 
number of recently discovered hydrocarbon 
compounds. One of these shows the phe- 
nomena so strongly that the name fluorescine 
has been given to it. Some of these sub- 
stances are used in photography in the prepa- 
ration of the so-called ortho-chromatic plates, ; sound scientific principles to popular language 
by which colored objects may be photo- 
graphed in their proper relations of light and 
shade, without the disturbing effect of the 
varying actinic power of the different colors. 
Glass colored yellow by uranium is highly 
fluorescent, and characters traced on paper 
with a solution of stramonium are almost 
invisible in daylight, but appear instanta- 
neously when illuminatfed with the flame 
of burning sulphur. The distance on either 
side of the light spectrum at which these 
invisible ether-waves may be found is im- 
known, but it must be very great. A spec- 
trum has been obtained from the electric 
light six or eight times as long as the ordinary 
visible one, and these waves may exert a 
distinct influence in many ways of which, at 
present, we have no comprehension. Thev 
may even produce sensations in some of the 
lower forms of life of which we can form no 
conception, just as certain persons can hear 
acute sounds to which others are deaf. The 
whole subject of radiant energy — which 
includes light, heat, electricity, actinic force, 
and probably many other forms — is just 
beginning to be comprehended, and no one 
can say to what revelations the future stud}" 
of the subject may lead us. 
[Specially Reported for Tlie Popular Science News.] 
THE BRITISH ASSOCIATION AT NEW- 
CASTLE. 
The last meeting of the British Association for 
the Advancement of Science, at Newcastle, has 
left, both upon scientists and their hosts, an im- 
pression of unwonted success. The social arrange- 
ments have been all that could be desired, and the 
excursions admirable in every respect, — that of 
Saturday (to the city of Durham) being made mem- 
orable by the conferring of the honorary degree of 
Doctor of Civil Law upon the officers of the Asso- 
ciation. This imposing ceremony took place in 
the chapter library of the Cathedral, within whose 
lady chapel repose the bones of the venerable Bede, 
England's first historian. The decorated shrine 
that once adorned the spot has long since passed 
awaj", leaving only a marble slab with the inscrip- 
tion : " Ilac sunt in fossa Beda venerabilis ossa." 
Gratifying as it was that one learned body should, 
with all pomp of circumstance, show its appreciation 
of another, it was still more gratifying to the Asso- 
ciation to receive in Newcastle itself — a district 
owing its prosperity to the practical applications of 
science — distinct acknowledgments of the value of 
abstract investigations apart from their immediate 
utility. These were rendered by the Mayor on 
more than one occasion, the most impressive being 
that of Mr. Baker's lecture on the Forth Bridge, 
when the various trades companies of the city pre- 
sented an address to Professor Flower, as president 
of the British Association, recognizing that only as 
the result of long series of complicated researches, 
undertaken solely for the discovery of truth, has this 
triumph of engineering skill been possible. 
Mr. Baker's lecture on the Forth Bridge was one 
of three provided by the Association for what are 
termed the working classes, the object being to 
return some of the courtesies of the city by fostering 
The appreciation of an account of this stupendous 
enterprise by its chief engineer, had been shown 
beforehand by S,ooo applications for tickets, when 
only 3,500 could be allotted ; and the workingmen 
assembled in the hall, repeatedly, and with intense 
enthusiasm, expressed their intelligent interest in 
Mr. Baker's clear explanations and magnificent 
series of lantern illustrations. Scarcely less attrac- 
tive did the " Hardening and Tempering of Steel" 
prove in a district where the use of steel is of such 
great importance; and in developing his subject. 
Professor Roberts-Austin emphasized the absolute 
dependence of industrial progress upon the investi- 
gations of pure science. Pure science, itself, was 
also presented to a large and attentive audience by 
Mr. Walter Gardiner, who, in his practical illustra- 
tions and examples of " How Plants Maintain 
Themselves in the Struggle for Existence," gave a 
memorable lesson in Darwinism, and one much 
needed just now, when scientific terms and phrases 
are entering common speech without carrying with 
them the definite ideas to which in scientific use 
they are attached. 
Truly, Darwinism was in the air at Newcastle, 
forming, under one aspect or another, the great 
discussion of the meeting. In his presidential 
address on the first evening. Professor Flower, after 
making most practical suggestions on the arrange- 
ment and preservation of natural history collections, 
— a subject on which he, as director of the Natural 
History Department of the British Museum, must 
command the attention of all who would present 
their specimens to the best advantage, — brought the 
weight of his vast biological knowledge to the con- 
sideration of recent criticisms of Darwin's great 
hypothesis. Taking for granted that few, if any, 
original workers at any branch of biology now 
entertain serious doubt of the doctrine of evolution, 
and that all recognize an innate tendency in every 
organic being to vary from the standard of its 
predecessors, he discussed the agents by which, 
when it has asserted itself, this tendency is con- 
trolled or directed in such a manner as to produce 
the permanent, or apparently permanent, modifica- 
tions of organic structures which we see around us. 
In opening their respective sections on the following 
day, Professor J. S. Burdon Sanderson directed the 
attention of biological workers to fundamental 
questions in physiology bearing on the elementary 
mechanism of life, the problems of which most 
urgently need solution; while Sir William Turner 
called on his large audience of anthropologists to 
consider the question of a physical basis for heredity 
(the perpetuation of the like), and for variability 
(the production of the unlike), especially in its 
bearing on the transmission from parents to otf- 
spring of characters acquired by the parent. This 
latter topic, which just at present is greatly moving 
the biological world, came up for full discussion on 
Friday, in connection with papers from Mr. Poulton 
on "Acquired Characteristics," from Mr. Francis 
Galton on " Feasible Experiments on the Possibility 
of Transmitting Acquired Habits by Means of In- 
heritance," and from Professor Osborn on the 
pala^ontological evidence in this direction. Again 
was it brought up on Monday, in a large assembly 
of biologists and anthropologists, by Mr. G. J. 
Romanes in a paper on "Specific Characters," 
many men of world-wide reputation taking part in a 
debate presided over by Canon Tristram, the first 
church dignitary and almost the first naturalist to 
accept the then new and unpopular doctrine of 
Darwin. 
But Darwinism, though the greatest, was by no 
means the only subject to excite wide interest, even 
an intelligent interest in science through the 
addresses of specialists who know how to reduce ' in the sections of biology and anthropology, in the 
