602 NATURE 
[Jury 29, 1915 

A NEW SACCHARIMETER. 
NE of the many optical instruments which the 
English opticians have allowed the Germans to 
supply almost entirely is the saccharimeter. This 
instrument used to be made by Browning, but in late 
years nearly every instrument purchased in England 
has come from Berlin from the firm of Schmidt and 
Haensch, who make several designs of large and 
small instruments. It is therefore a pleasure to find 
an English firm—Messrs. Bellingham and Stanley, of 
London—making a saccharimeter which introduces 
valuable improvements on the German design. The 
one to which we refer is of the half-shadow type 
with quartz compensating wedges, but instead of the 
usual long wedge of which the movement is read 
direct by a scale and vernier, this one has a short 
wedge of larger angle. The wedge is moved by a 
screw, and the movement is read on a _ large 
drum with an open scale and_ sliding pointer. 

New short-wedge saccharimeter. 
The whole length of the scale is some 2 ft. 
instead of 14 or 2 in., and it can thus be read with 
great ease. 
In instruments making use of a quartz wedge of 
the usual length (about 3 cm.), the scale is nearly 
always uneven, and unless calibrated introduces errors 
amounting to several tenths of a degree Ventzke. 
According to Landolt this is due to the quartz, which 
he describes as ‘“‘a poor material optically”; he says 
that one seldom finds faultless plates, and that a pure 
wedge 3 cm. long is rare. Hence the value of the 
short wedge of Bellingham and Stanley which is less 
than half the usual length. The advantage of such a 
wedge, even if the quartz is not of special quality, is 
greater than would appear at first sight, since the 
field is due to the average effect of the whole of the 
light passed through the wedge, and this average 
will vary evenly through the small change of area of 
the wedge due to its movement, and thus the scale 
will be regular in spite of variations in the quartz; also 
it is easier to get repeated readings, owing to the 
greater ease with which the setting can be made with 
the fine adjustment given by the series, as compared 
with the usual rack and pinion motion. In fact, the 
NO. 2387, VOL. 95] 


makers state that they have not detected any cali- 
bration errors in their instruments. 
Another valuable feature is the enclosure of the 
scale and all working parts, so that they are protected 
from the salt vapours. The importance of this needs 
no emphasis to those who have had experience with 
instruments of this character. The corrosion of the 
Ce i Ee Taser 
Scale of saccharimeter. 
metal work—especially steel work—and of the scale, 
when as in the higher priced instruments this is 
engraved on silver or nikelin, under the action of the 
fumes in a laboratory often renders the instrument 
almost unusable in a few years. 
The instrument is mostly con- 
structed of an aluminium alloy, 
protected by a_ black-stoved 
enamel, and no steel is used 
except for a small spring, which 
is entirely enclosed. 
The optical work is of the 
first quality. The dividing line 
is sharp and clean, and the 
field evenly illuminated, so 
that adjustment for equality 
can be made without 
ambiguity, and with  corre- 
sponding accuracy. The 
makers calibrate the scale at a 
number of points by direct 
reading against a_ polariser 
rotated on a divided circle. In 
the instrument examined the 
divisions were in half degrees 
‘““Ventzke”’ (of which 100 corre- 
spond to 34-68° of arc, for 
sodium light at 17-5° C.), and 
it was easy to estimate to 
tenths of a degree, i.e. to less 
than three minutes of are. 
The design and workmanship 
were all that could be desired. 
The same firm is also making refractometers of the 
Abbe and Pulfrich type and other optical instruments. 

OUR OVERSEAS MUSEUMS. 
HE British Museum, the parent and model of the 
museums scattered throughout our Empire, 
stands alone in that it has no journal of its own 
wherein to record the work done by its staff, though 
from time to time special memoirs and reports are 
published by the Trustees. There is much to be said 
for the publication of a museum journal, and not the 
least important of its functions would be to afford 
the general public an index of the magnitude and 
scope of its work, which can now only be 
estimated by laborious compilation from the annual 
“‘blue-book ” or the publications of the various learned 
societies. 
A measure of the nature of the work performed 
by the staff of a properly organised museum can be 
gauged by a survey of the journals and ‘‘records” 
relating to the museums of our colonies and of our ©» 
Indian Empire. For the most part the contents of 
such journals are of necessity of a highly technical 
