138 Progress in Science . [January , 
known, and will effectually protect the more brittle liquid glue, Gold-size is 
rapidly acted upon by glycerine, but when protected with a good coating of 
shellac is perfectly sate. Too much care cannot be taken in washing and 
cleaning the surfaces to be varnished from the least trace of adhering glycerine : 
the entire success of the process, as before mentioned, depends upon minute 
attention to this point, and if carefully carried out success is certain. The 
writer has objects mounted in glycerine fifteen years ago free from any trace of 
leakage. Liquid glue is also effectual in varnishing preparations mounted in 
castor oil : this useful medium has been much neglected, owing to the difficulty 
of preventing leakage. The cell and cover should be cleaned, as before men- 
tioned, but, instead of water, benzole — carefully applied with a brush — must be 
used for the removal of the oil remaining after the application of the blotting- 
paper. The shellac varnish is to be followed by gold-size, as in the case of 
glycerine mounting. 
A new method of measuring the absorption-bands in spectra has been com- 
municated to the Royal Microscopical Society by Mr. H. C. Sorby. The 
apparatus consists of a crystal of quartz, cut so that the light passes along 
the line of the principal axis: the thickness used is exactly inches. This 
crystal is placed between two Nicol prisms, the upper one capable of rotation 
for the purpose of adjustment ; the lower one fixed to an ivory circle, 2^ inches 
in diameter, each half of which is divided into ten parts, and these again into 
five smaller divisions, so that there is no difficulty in reading off to i-iooth of 
a half revolution. The light passing through this apparatus, when viewed 
with the spectroscope, divides the spedrum into eight spaces by seven well- 
defined bands, which in a prism spedrum are apparently at very uniform 
intervals, but at a much less wave-length interval at the blue than at the red 
end. When the apparatus is attached to the micro-spedroscope, the pointer 
of the circle being placed at zero, the upper prism is rotated so that the centre 
of the second dark band from the red end of the spedrum exadly coincides 
with the sodium line, or with the solar line D. Adi the other dark bands are 
then in perfedly constant and definite positions, depending on the adion of 
quartz on light of various wave-length. On rotating the ivory circle each band 
gradually passes from the red end towards the blue, until when the circle 
comes to the next zero point, commencing the next semicircle, the series of 
bands is exadly the same as at first. The formula for reducing the degrees of 
the scale to their respedive wave-lengths is given, and also a table for an 
instrument construded with a crystal of quartz of exadly inches in thick- 
ness, cut and mounted as described. The chief objedions to the apparatus 
appear to be the difficulty of obtaining and cutting a suitable piece of quartz, 
and also the size of the apparatus, its length being about 3^ inches, which 
renders the instrument inconvenient for attachment to the ordinary micro- 
spedroscope, but it has answered well placed below the stage of Mr. Sorby’s 
binocular spedrum microscope. 
The Quekett Microscopical Club have issued a Catalogue of the prepara- 
tions in their cabinet, containing the total number of 2041 slides. The 
subjeds most largely represented are — Hairs of animals, of which there is a 
colledion of 238 specimens, including a very complete series from Indian and 
other bats ; the seeds amount to 217 — these and the greater part of the hairs, 
especially those from India, were the gift of Dr. M. C. Cooke, as also most of 
the microscopic fungi, of which there are 6g specimens ; the ferns are well 
represented by 171 slides. The objeds can be borrowed for examination by 
members, under certain conditions, offering great facilities to those who wish 
to compare at their leisure a series of specimens. The whole colledion has 
been formed by the liberal donations of members of the Club, and it is to be 
hoped that the annual increase may be a large one, which will certainly be 
the case if mounters of objeds will send their duplicate specimens to the 
cabinet. 
An ingenious little instrument, for readily cleaning very thin covering-glass, 
has been contrived by Mr. W. W. Jones, of the Quekett Microscopical Club. 
It consists of a small tube of brass or steel, of about an inch in diameter and 
