Nov. 17, 1881 | 
NATURE 
55 
the last square being almost opaque, and representing twenty- | 
five thick: esses of tissue paper. The exposure in every case was 
ten seconds; the distance of the film from one light or lights 
always 14 feet, and the number of cells 30. The develop- 
ment was confined to two minutes exactly, an oxalate developer 
of normal strength being employed ! :— 
Result of First Experiment 
No. of square 
thr-ugh which the 
light penetrated. 
Group of four lamps (Nos. 1, 2, 3,4) ... .. 13 
5 three ,, (Nos. 2, 3, 4) Boe acre elk} 
aA twos (NOS 354)) sea) “eo ee" 10, 
5 one lamp (No. 4, low resi: tance) 23 
op 6 (No. 3, high resistance) 20 
As it was a matter of difficulty to judge the exact square or 
number printed through, the mean results of three ob ervers or 
readers was taken. So that the development should be the same 
throughout, all plates were developed simultaneously in the same 
dish. 
The result may not permit us to estimate with scientific accu- 
racy the value of the lights under che above conditions, but it 
proves practically (1) that the amount of light given off by 
four lamps is less than that given by three, and that the elec- 
tricity is employed most economically for lighting when only 
one lamp is used ; and (2) that, at any rate in the conditions 
described, a comparatively low-resistance lamp gives more light 
than a comparatively high one. 
In my second experiment I estimated the actinic power of 
single lamps, when one or more were in circuit, the photographic 
arrangements heing the same. 
Result of Second Experiment 
No. of square 
through which the 
light penetrated. 
One lamp, No. 4 (only one in circuit)... ... 23 
One lamp, No. 4 (two incircuit) ... ... ... 18 
One lamp, No. 4 (three in circuit)... ... ... 14 
One lamp, No. 4 (four in circuit) ... ...  «.. 
Are light (with 30 cells) upwards of 25 
Ordinary fish-tail burner (burning 5 cubic feet 
per hour) Ais. dot Pacey COO Coda eecee 
The result here is interesting in showing the comparative 
strength of the lamps by themselves, and to what extent the livht, 
so to speak, is ‘‘ turned down” by bringing another lamp into 
circuit. As my screen was only graduated as far as 25, it was 
impossible to estimate the comparative value of the arc light, 
for it went above this degree, while a low-resistance Swan lamp 
only goes as far as 23. This last lamp, No. 4 in the series, was 
the one always tested, and therefore the re:ults shown m:y be 
considered the most favourable. The result given by a good 
fish-tail burner permits us to make some comparison between 
gas and the Swan light at a minimum. 
It says something for the skill with which the sensitive gela- 
tino-bromide is prepared commercially nowadays, when we find 
it is so uniformly sensitive that in the two trials (where square 23 
is recorded) there should be so unanimous a result. 
Noven.ber 12 H. BADEN PRITCHARD 
Sound-producing Ants 
REFERRING to Mr. Blanford’s letter in NATURE, vol. xxv. 
p. 32; whilst lying awake early one morning before the servants 
were stirring, when camped in the Deccan at the present small 
station of Chota or Chick-Soogoor, on the G.I.P. Railway, 
during the winter of 1868-69, I heard a sound, as Mr, Blanford 
suggests, repeated at regular intervals of about a second. It 
sounded as though the wall of the tent was being struck by a 
light fringe along one side; but noticing that the air was per- 
fectly still, I listened for some minutes, wondering what it was 
and trying to fix the locality. I got out of bed cautiously and 
looked out ; the whole of one side of the tent for a height of two 
feet was covered with white ants so thickly that at the first 
glance I thought the wall was covered with a grey-reddish mud 
to this height. I was trying to make out how the sound could 
be produced, when it stopped suddenly, the an's evidently 
having become aware of my presence ; they then began to clear 
off the wall rapidly, and in a few moments it had become white 
again, They had not attacked the cottonwall. On looking at 
* Developer :— 
Saturated solution of oxalate of potash 
os 3 parts. 
Saturated solution of proto-sulphate of iron... 1 + 
I part. 
the ground round the tent I found their runs extending from a 
tamarind tope, the nearest trees of which were about 50 feet 
away. The runs were built in the usual way of red Deccan soi), 
there were great numbers of them, varying in width from the 
thickness of twine to 24 inches, often crossing each other 
diagonally. No dcubt the ants had found the tent in the 
evening, and were prepared to make a morning meal of a 
portion of it, when I disturbed them on looking out. The im- 
pression on my mind at the time was that the whole body of 
ants struck the tent wall at the same time with their heads, and 
that it was very extraordinary that they all stopped at once ; 
there were no dropping shots, it was an instantaneous cessation 
along the whole line. The tent, which was a double one, was 
at least 30 feet long, and the ants possibly extended round the 
ends. JOHN FOTHERINGHAM 
13, Springfield Road, N.W., November 12 
UNIVERSITY COLLEGE, LoNDON.—The Calendar will give 
you all the information you want. 
‘‘Firty YEARS’ WoRK OF THE GEOGRAPHICAL SOCIETY.” 
—We believe Mr. Markham’s narrative may be ordered through 
any bookseller. The Polar Observing Station at Lady Franklin 
Bay was really occupied by a United States party in the past 
summer, with the intention of carrying on cbservations for at 
least a year, 
SEALS IN LAKE BAIKAL.—Mr. Edward Fry refers Mr. Keane 
to Bell’s ‘‘ British Quadrupeds,” 2nd edit. p. 248, where he 
will find that Herr Radde figures and describes the seal of Lake 
Baikal in his ‘‘ Reise im Siiden von Ost-Siberien’’; and to 
Murray’s ‘Geographical Distribution of Mammals,” p. 126. 
Mr. Thomas Ward sends the following references :—Myer’s 
‘© Geography, vol. ii. p. 9, edition 1829 ; Erman’s “‘ Travels in 
Siberia,” vol. ii, p. 2co (Cooley’s translation); ‘‘ English 
Cyclopzdia” (Article Baikal), From this last Mr. Ward quotes 
as follows :—‘* The existence of the salmon, of the seal, and of 
a kind of sponge in the fresh water of the Baikal has given rise 
to many speculations among naturalists. Pallas and Georgi are 
unable to explain this phenomenon otherwise than on the sup- 
position that the Lake of Baikal at some remote period formed 
a part of the Northern Ocean, . . . or on another supposition, 
that these animals were transported into the lake by some ex- 
cessive inundation of the Lena River, whose sources are not far 
from its western borders.” 
HEADS AND HATS 
E have received the following further communications on 
this subject :— 
HavinG last March laid the subject referred to by your cor- 
re:pondents, Messrs. Kesteven and Hyde Clarke, before the 
Bristol Naturalists’ Society in a short paper, I venture to offer 
a résumé of the facts collected by my friend Dr, Beddoe and 
myself, which seem to justify the conclusion that a diminished 
size of hat is now required by young men as compared with those 
used by the same classes twenty to twenty-five years ago. (I) 
I have from time to time during the last three or four years had 
my attention called to this alleged change ty Mr. R. Castle, 
hatter and hosier of 1, St. Augustine’s Parade, Bristol, who, in 
proof of it, has frequently shown me hats of small size, such as 
are now generally required by both gentlemen and_ servants 
tetween the ages of twenty and thirty. He states that these 
smaller hats, which w ed to con ti‘ute only a small percentage of 
his <t-ck, now form the bulk of it, whilst those which formerly 
suited the larger proportion of his customers are now usually 
required only by the older ones amongst them. Mr. Castle 
estimates the difference as amounting to at least one whole size, 
which is equivalent to three-eighths of an inch in circumference, 
and he has furnished me with typical extracts from his order 
book to Messrs, Lincoln and Pennett in fuller proof of his 
assertion. I have arranged and reduced his figures in the 
accompanying table, and the result does undoubtedly seem to be 
that the buyers of 1875-80 are taking a hat at least one size 
smaller than the same c/ass (not necessarily the same individuals) 
used to do twenty to twenty-five years previously. (2) My 
friend Dr. Beddoe, whose attention I called to the subject last 
year, informed me that Mr, C. Garlick, hat manufacturer 
of 87, Castle Street, Bristol, furnished him w ith the sizes of 
200 hats sold by him in 1862, and the average is precisely 
7, one of the lots yielding 7°01 and the other 6°99, Two 
