NATURE 
=s 
on the glacial theory in his various writings on glaciers, is in 
marked contrast to the ignorance of the true state of the case 
usually displayed by English authors, who ascribe to Forbes the 
sole credit of all recent progress in the glacial theory. 
Forbes’s work commenced in 1841 ; it was in that year that 
he made his memorable visit to the Glacier of the Aar, and there 
found Agassiz, who had at that time already spent five summers 
in the study of glaciers, and published in 1840 the preliminary 
part of the investigations carried on by himself and his com- 
panions (*‘ Etudes sur les Glaciers”). 
Agassiz with his usual freedom in dealing with his associates, 
which has so often made him appear as following the lead of his 
pupils, freely imparted to Forbes all he had seen, and certainly 
-had no idea that the hospitality so freely proffered would be 
returned by the proceedings of Forbes, who appropriated what 
he could, and misrepresented the nature of his intercourse with 
Agassiz while his guest on the Glacier of the Aar. 
To Tyndall we owe a thorough sifting of the claims of each 
investigator on the subject, and however unpalatable it may be 
to national prejudices that the name of Forbes should play a 
secondary part in these investigations by the side of those of 
Venetz and Charpentier, Rendu and Agassiz, the fact remains 
the same, and every fair-minded investigator will thank Tyndall 
for what he has done. ALEX. AGASSIZ 
Cambridge, Mass., April 15 
Scientific Endowments and Bequests 
In the article on scientific endowments and bequests in NATURE 
for April 24, there is a statement, in reference to the Trinity 
Natural Science Fellowship, which perhaps requires a little 
correction. 
Although there can be no doubt that the proposed new scheme 
for the selection of a fellow is in every way better than the old 
system of selection by routine examination, it is hardly right to 
speak of the election of a Natural Science Fellow, which took 
place in October 1870, as an ‘‘ unsuccessful experiment.” 
It is certainly much to be regretted that circumstances have 
prevented the gentleman then chosen from strengthening the 
staff of scientific workers and teachers at Cambridge ; but it is 
equally certain, that no system of selection that could possibly 
be desired, would have resulted in the election of a man possessed 
at once of more promising scientific abilities, and of a more 
genuine love for science. 
The writer of the article seems to think that the examiners on 
that occasion were in search of what he is pleased to call a 
* genuine zoologist ;” there is no doubt that there was then as 
there is now, a striking absence of young men of ability, devoting 
themselves to zoology ; but though the college had announced 
a preference for a physiologist, yet the examiners were em- 
powered to recommend either a zoologist, or one following any 
other branch of natural science. F, M. BALFour 
Trinity College, Cambridge, April 20 
Permanent and Temporary Variation of Colour 
in Fish 
ONE or two episodes in the annals of the Brighton Aquarium 
for the week just ended deserve a passing note. 
Among the Plaice, Pleuronectes platessa, added to the general 
collection, is one remarkable example, having the pos- 
terior half of its under surface, usually white, coloured 
and spotted as brilliantly as the upper one; the line of 
demarcation between these two colours again, though sinuous, 
is most abrupt, there being no shading through from one to the 
other as might have been anticipated. This specimen may be 
turned to good account by advocates of the Darwinian theory, ‘as 
affording a remarkable instance of the occasional tendency of a 
specially modified type to revert to its primeval state—the Pleuro- 
nectidze being derived from ancestors originally possessing bilateral 
symmetry, and an equal degree of coloration on each side. 
As the spawning season advances, many of the fish, and more 
especially certain of the Acanthopterygian order, undergo various 
important modifications in both their habits and appearance. 
During the last week or so, many of the larger examples of the 
Black Bream, or Old Wife (Cantharus lineatus), exhibited in 
tank 4 on the north side of the Western corridor, have afforded 
a striking illustration of these phenomena. Hitherto their 
prevailing tint has been a delicate silvery blue, varied by irregular 
longitudinal lines of pale yellow, a hue scarcely in harmony with 
| the name by which they are most popularly known. These light 
colours have now disappeared, or rather become absorbed, in a 
prevailing shade of deep leaden black, which, while deepest on 
the back, spreads itself over the whole surface of the fish with 
the exception of a few transverse lighter bands in the region of 
the abdomen. The males in particular are most conspicuous for 
this change, and these retiring from the remainder of the shoal, 
select certain separate and prescribed areas at the bottom of the 
tank, where they commence excavating considerable hollows in 
the sand or shingle, by the rapid and powerful action of the tail 
and lower portion of their body. A depression of suitable:size 
having been produced, each male now mounts vigilant guard 
over his respective hollow, and vigorously attacks and drives 
away any other fish of the same sex that ventures to trespass 
within the magic circle he has appropriated to himself. Towards 
his companions of the opposite sex his conduct is far different ; 
many of the latter are now distended with spawn, and these he 
endeavours by all the means in his power to lure singly 
to his prepared hollow, now discovered to be a true nest- or 
spawning bed, and there to deposit the myriad ova with 
which they are laden, which he then protects and guards with 
the greatest care. Whether the aggregated produce of 
a large number of females is thus consigned to one bed, and 
whether the ova are guarded by the male until the young fish 
make their appearance, are points which, while awaiting con- 
firmation, may be almost confidently inferred, reasoning from 
the very analogous nest-forming habits of the Gusterosteide or 
+ Stickleback family, already so familiar to every naturalist. The 
male of the Lump fish (Cyclopterus lumpus) is said to watch 
over the spawn of the female in a very similar manner, and at 
the particular time of the year, early spring, whenit is deposited, 
assumes the most lively tints of red and blue, which disappear 
again after his paternal duties have been discharged, and are not 
retained through life as has been formerly supposed. On this 
point we have direct evidence from specimens confined within 
the aquarium walls. For yet another instance of change of 
colour in the male fish, associated with its nest-forming habits 
in the same Acanthopterygian order, I am indebted to a recent 
visit to the aquarium at the Crystal Palace, where Mr. Loyd 
directed my attention to a male example of the Cuckoo Wrasse 
(Zabrus mzxtus), which had formed a deep hollow in the sand of 
its tank, and was endeavouring in the most persuasive manner to 
induce a female of the same species to share it with him, swim- 
ming backwards and forwards between her and the completed 
nest, and plainly exhibiting the greatest anxiety for her to 
follow. The normal brilliancy of this fish was supplemented by 
a light opaque patch that extended over a considerable portion 
of the back of his head and shoulders, while the tints of the 
remaining portion of the body were more than ordinarily 
deepened. 
W. SAVILLE KENT 
On Approach caused by Velocity and Resulting in 
Vibration 
Pror, J. CLERK-MAXWELL, in his recent paper on ‘‘ Action 
at a Distance,” has brought under notice again the experiments 
of Prof. Guthrie ‘‘On Approach caused by Vibration,” and has 
so well summarised in popular language the facts investigated 
and the conclusions arrived at, that fitting opportunity appears 
to present itself to me for calling the attention of the scientific 
world to phenomena closely allied to those under review although 
more complex in their manifestation, since in these velocity is 
independent of, yet initiates vibration. That they have not been 
referred to in the experiments either by Prof. Guthrie, Challis, 
and others who have taken part in the discussion is probably to 
be accousted for in the unfortunate although convenient habit 
indulged in by experimentalists of using the tuning fork as the 
agent for demonstration. 
The following passage from Prof. J. Clerk-Maxwell’s paper 
alluded to will best introduce my own observations—‘‘ Here is a 
kind of attraction with which Prof. Guthrie made us familiar. 
A disc is set in vibration and is then brought near a light sus- 
pended body which immediately begins to move towards the 
disc as if drawn towards it by an invisible cord. What is this 
cord? Sir W. Thomson has pointed out, that in a moving fluid 
the pressure is least where the velocity is greatest. The velocity 
of the vibratory motion of the air is greatest near the disc. 
Hence the pressure of the air on the suspended body is less on 
the side nearest the disc than on the opposite side ; the body 
yields to the greater pressure and moves towards the disc. The 
