DW ATROT LE 
[ Marcu 14, 1907 
472 
of Loch nan Gabhar, a little weedy hollow only 5 feet 
deep, which is evidently being rapidly silted up. An 
interesting account is also given of the Red Lochan at 
Tulloch, a small pond lying in an extensive morainic 
terrace near the north end of Loch Treig, called in Gaelic 
by a name signifying ‘“‘ brown eye.”’ It is only about 
30 yards in longest diameter and 5 feet deep in the centre, 
fed only by rains, and, though it has no outflow except 
by percolation through the gravel, its surface is maintained 
almost constantly at the same level. The water is always 
turbid, and varies in colour from dull green to brown or 
red. When examined in May, 1902, the water was brown, 
the collection with the coarse net was pale yellow, while 
that taken by the fine net was decidedly red; there were 
only two abundant organisms, the larva of an insect 
(Corethra) known as the ‘* phantom larva,”’ and a reddish- 
coloured rotifer, Anuraea valga, to which the colour of the 
water was evidently due, for none of the other organisms 
were abundant enough to be held responsible for the colour 
of the water. On placing the collections in formalin, a 
blood-red sediment was deposited, which was found to 
consist chiefly of Anuraea valga and myriads of its red 
Examined subsequently at different seasons, the 
changes of colour were doubtless correlated with the pre- 
dominance of one or other organism. None of the other 
ponds in close proximity shared the turbidity and reddish- 
brown colour of the Red Lochan, the peculiarity being 
probably due to its being more closely shut in, the surround- 
ing rim of gravel being 14 feet or more above the pond, 
and there is besides a fringe of birch trees. The water is 
stagnant, which favours the growth of certain organisms, 
particularly Anuraea valga. It is said that wildfowl never 
settle on the pond, and that the common frog cannot live 
in it. The following legend was related to Sir John 
Murray concerning this Red Lochan :—‘ Many centuries 
ago there lived in these parts a noted hunter named 
Donnuil. In return for some services rendered to the witch 
of Ben-a-Vreich, she offered to deprive the deer of the 
sense of sight or of smell, so far as he was personally 
concerned. He chose to have the deer deprived of the 
sense of smell, ‘ for,’ said he, ‘I can easily cheat their 
eye.’ The witch, however, told him that in the stomach 
of the last stag he would kill there would be found a ball 
of worsted thread. As time passed Donnuil became ill, and, 
while weak in bed, his daughter told him a fine stag was 
caught by the horns in some bushes near the house. He 
asked for his cross-bow, and, although in bed, he shot 
the stag through his bedroom window. Later on his 
daughter brought him a ball of worsted which had been 
found in the stomach of the stag. He knew his end was 
near; indeed, he died the same evening. On the following 
morning the Red Lochan had appeared at the place where 
the stag was killed.” 
The paper concludes with some interesting notes on the 
biology of the lochs by Mr. James Murray, who found 
that “the plankton of Loch Lochy offered a remarkable 
contrast to that of Loch Ness, though the conditions 
seemed so similar, the quantity in Loch Lochy being 
many times greater and the species more numerous, but 
the special feature was the quantity and variety of the 
phytoplankton. In Lochan Linn da-Bhra the Diaptomus 
was so deep red that when the nets were drawn from 
the water they seemed to contain blood; the same 
peculiarity was observed in An Dubh Lochan, but in a 
lesser degree. 
The paper is illustrated by coloured maps showing the 
bathymetry and orography, and there are several wood- 
cuts in the text, some of which are reproduced in this 
notice. 
eggs. 
THE STRUCTURE OF METALS.: 
"THE lecturer said that his purpose was to give some 
account of researches in which he had been engaged 
for a good many years, dealing with the manner in which 
metals were built up and the manner in which their struc- 
tures allowed them to yield when they were compelled to 
change their shape by being overstrained. A piece of 
metal was not a homogeneous single thing; it was a 
1 Abstract of ‘* Wilde” Tecture, delivered hy Dr. J. A. Ewing, F.R §., 
before the Manchester Literary and Philosophical Society on February 18, 
1950, VOL. 75 | 
collocation of grains or granules, which built it up just 
as granules of ice built up a glacier. The grains of metal 
were irregular in shape and unequal in size. Their 
existence was revealed by polishing and etching the sur- 
face of the metal and examining it under the microscope, 
when the grains could readily be distinguished by differ- 
ences of texture, and the boundaries between them could 
be clearly traced. Investigation showed that each grain 
was, in fact, a separate crystal, and the irregular 
boundaries. were due to casual inequalities in the rates at 
which the various crystals had grown during their form- 
ation, which might occur when ‘the metal was solidifying 
from a fluid state, or when it passed in the solid state 
through certain temperatures at which re-crystallisation 
took place. Each grain might. be regarded as composed 
of an immense number of molecular brickbats grouped in 
perfectly regular tactical formation, but the direction in 
which these brickbats were piled was different in different 
grains; hence on being etched the polished surface showed 
differences in texture and in behaviour as to reflecting 
light. Microscopic photographs illustrating these features 
in iron and other metals were exhibited. 
When the metal was strained beyond the elastic limit, 
and thereby compelled to change its form, the change of 
form took place by slips occurring between the layers of 
molecular brickbats in the individual granules. The dis- 
covery of these slips had been made by the lecturer in 
conjunction with Mr. Walter Rosenhain, by noticing 
certain lines to appear on the polished surface of a piece 
when subjected to severe strain. These‘ lines, which they 
called slip lines, looked like minute crevasses, but were 
really steps caused by the slipping of one layer on its 
neighbours, just as cards might slip in a pack. In any 
one crystal grain there were at least three sets of in- 
dependent parallel planes in which such slips could take 
place, and these allowed the grain to undergo complete 
alteration of form as a result of the straining. Micro- 
scopic photographs were exhibited showing three systems 
of slip lines on the surface, corresponding to slips in three 
directions throughout the substance of the grain. The true 
nature of these slip lines was made apparent by means of 
obliquely incident light, which showed them as little steps 
in the surface. An interesting direct confirmation of this 
had been afforded by recent experiments of Mr. Rosen- 
hain in which cross-sections of the stepped surface had 
been obtained. 
Dr. Ewing next explained, by aid of models, a theory 
which he had recently advanced as to the structure of the 
crystal granule itself. This theory might be regarded as 
an extension of the views he put ferward fifteen years 
ago to explain the phenomena of magnetic induction by 
the mutual actions of polarised magnetic molecules. 
Cohesion in the crystalline structure might similarly be 
regarded as due to the mutual forces’ between polarised 
molecules, the polar quality of which determined the 
regular tactical formation in which they grouped them- 
selves to form the crystal. For this purpose he conceived 
of each molecule as possessing polarity along each of 
three rectangular axes; in other words, as having six 
poles exercising forces of attraction on the opposed poles of 
neighbouring molecules. 
The lecturer proceeded, by aid of the model, to demon- 
strate the process of crystal-building with these polarised 
molecules for brickbats. He showed how, under certain 
conditions, a group of dissenting molecules might be 
formed within the crystal grain, possessing a certain degree 
of stability, though not in complete harmony with the 
molecules around them. Evidence for the existence of 
such groups was furnished by the microscope in the ex- 
amination of iron and other metals. The process of 
straining was next considered, and it was shown that the 
conception of polarised molecules was in agreement with 
what was known of the actual behaviour of metals during, 
first, the «lastic stage of straining. and, second, the stage 
where much greater yielding tock place and permanent 
set was produced. The molecular theory explained how 
energy was dissipated in the process of straining, and also 
how elastic “‘ fatigue ’’ resulted. After any severe strain 
the piece was a long time in recovering its full amount 
of elastic quality, but the recovery could be accelerated 
by heating it. These phenomena were accounted for by 
\ 
