NORTHERN SOCIETIES, 135 
upon the object with a gradually increasing obliquity until, when 
the instrument is nearly horizontal, a perfect dark ground illumina- 
tion can be obtained even with the highest power, while the 
gradual way in which the light becomes more and more oblique 
immediately under the eye, and the capability of arresting the in- 
clination at that point where the most suitable illumination for the 
object under examination is obtained, give to the observer powers 
he has never before had at his command in any form of microscope 
yet produced. 
The horizontal rotation mentioned above allows the object to be 
directed to the light at every angle in azimuth—to borrow a term 
from the astronomer—as the cradle-joint on the top of the pillar 
gives every angle in altitude, as the object occupies the centre of 
both motions by a combination of the two, it can of course be 
placed in every possible position, ‘These angles are read—the 
latter by a graduated circle in the outerside of the cradle-joint, 
giving the inclination of the body to the vertical; the former by 
means of the graduated circle at the foot. Readings of these 
circles being taken with the mirror placed as above described at 
any time by so fixing the instrument that these circles read the 
same. Any desired effect will be exactly reproduced, wherever the 
lamp may be placed—a point of the greatest importance to workers 
with high powers. 
There is a third divided circle on the substage axis, giving the 
inclination of the substage to the axis of the body. A strong 
clamp on the outerside of the cradle-joint holds the body firmly at 
any inclination, and a graduation on the slide of the coarse adjust- 
ment enables the working distance of the objectives to be measured 
and compared. 
Upon this stand, and with one of their best ths objectives, 
Messrs. Watson easily resolved in our presence Pleurosigma 
angulatum : not into lines merely, but into dots or hemispheres, 
which is rather a severe test for such an objective. 
With these exceptions there appeared to be nothing really new 
in London. 
NORTHERN SOCIETIES. 
BOLTON Mricroscorrcat Society. Hon. Sec.: Mr. W. Rideout. Meets on Friday 
evening once in each month. 
CHESTER Natura Scienck Association. Hon. Sec. of Microscopical Section: 
Mr. J. D. Siddall. 
DONCASTER MrcroscopicaL Society. Hon. Sec.: Mr. M. H. Stiles. Meets 
twice in each month. 
HALIFAX. A Private Society. Members meet at each others houses. 
LEEDS. No Microscopical Society in existence, 
