AUGUST 25, 1899. ] 
It was only after much experimenting that 
Tyndall succeeded in obtaining absolutely op- 
tically-pure air, so clear that the path of even 
the most intense light is invisible. In experi- 
menting upon water Lallemand was unable to 
obtain optically-pure water, and was led to 
question its existence. Professor Spring, of 
Liége, has, however, succeeded in thus purify- 
ing water and an extended account of his work 
is given in the Bulletin of the Royal Academy 
of Belgium. That the visibility of the path of 
aray of light is due to suspended matter is 
shown by the fact that in the optically-pure 
water of Spring the path is wholly invisible. 
Such water cannot be obtained by distillation, 
nor by filtration, these processes having no 
tendency to purify water optically, but often 
rather the contrary. Optically-pure water can 
be obtained by the action of a weak high-ten- 
sion current on water which contains suspended 
matter, or by sedimentation of colloidal pre- 
cipitates, such as aluminum, ferric, etc., hy- 
droxids, or by filtration of the water through 
colloidal precipitates. Crystalline precipitates, 
such as calcium oxalate, have little or no effect; 
nor can organic liquids be purified by colloidal 
precipitation. Spring believes that the illumina- 
tion of the water is probably not caused by the 
dust itself, but by minute bubbles which adhere 
to the dust particles. These occasion different 
colors, in which red and orange predominate, 
and hence the blue color of natural waters can- 
not be due to a selective absorption on the part 
of the suspended matter. J. L. H. 
THE BRITISH MUSEUM. 
A RETURN dealing with the British Museum 
has been issued in the form of a Blue-book. We 
learn from a report in the London Times 
that it contains an account of the income and 
expenditure of the British Museum (Special 
Trust Funds) for the year ended March 31, 
1899; areturn of the number of persons ad- 
mitted to visit the Museum and the British 
Museum (Natural History) in each year from 
1893 to 1898, both years inclusive; together 
with a statement of the progress made in the 
arrangement and description of the collections 
and an account of objects added to them in the 
year 1898. 
SCIENCE. 
257 
Part VI. of the return, which gives an ac- 
count of the general progress at the Museum at 
Bloomsbury, states that the number of visitors 
to the Museum in the year 1898 is the highest 
on record since the year 1883, amounting to a 
total of 612,275, as against 586,437 in 1897. 
The visitors on Sunday afternoons numbered 
41,858, as against 37,594 in 1897. The total 
number of visits of students to the reading room 
during the year was 190,886, a slight increase 
on that of the previous year, which was 158,628. 
The daily average was 627, as against 624 in 
1897. The number of volumes, etc., supplied 
to readers in the year was 1,397,145, as against 
1,419,159 in 1897. There has been a marked 
increase in the number of visits of students to 
the several other departments other than the 
reading room. The total amounted to 48,214, 
as against 40,976 in 1897. This increase is 
partly to be attributed to the extension of 
students’ rooms. The new building commenced 
last year for the accommodation of the book- 
binders has been completed, and the bookbind- 
ing staff has been transferred thither. The 
basement rooms of the Museum which have 
thus been vacated are being fitted for the stor- 
age of newspapers. 
The part of the return relating to the British 
Museum (Natural History) states that the total 
number of visitors to the Natural History 
Museum in 1898 was 419,004, as compared with 
422,607 in 1897. The slight falling-off shown 
in these figures has taken place in the week- 
day visitors, the Sunday attendance for the year 
(50,432) being a little in excess of that for 1897. 
The average daily attendance for all open days 
during the year was 1,151 ; for week-days only, 
1,181; and for Sundays, when the Museum is 
open only in the afternoons, 970. The new 
whale room was opened to the public on Whit 
Monday, May 30, 1898, and has been much ap- 
preciated by visitors. A photographic studio 
has been erected at the back of the Museum. 
Renewed application has been made to the 
Lords Commissioners of the Treasury for funds 
for lighting the galleries and studies of the 
museum by electric light, and a sum of £2,000 
has been provided for 1899-1900 for the intro- 
duction of the light into the work rooms and 
studies. 
