112 
BRITISH ASSOCIATION.— 1835. 
Mr. Andrew Pritchard exhibited examples of various kinds 
of apparatus constructed by him for illustrating the Polarization of 
Light; and gave a brief account of his improved achromatic micro¬ 
scope, one of which was placed upon the table. 
The construction of a simple polariscope invented by Mr. Pritch¬ 
ard w r as explained. The crystals to be examined were mounted in 
slides and introduced between tourmalines, by which means sections of 
any crystals that present themselves may be examined, and the cell 
of the upper tourmaline being removeable can be employed for other 
experiments. A lens was attached for condensing artificial light. 
The mechanical part of the achromatic microscope produced was 
constructed on the principles recently published by Dr. Goring and 
Mr. Pritchard in their works on the microscope: the chief feature in 
the optical part was the execution of a set of object-glasses which 
admitted a pencil of light of sixty-eight degrees, free from spherical 
and chromatic aberration, having the oblique pencils nearly correct 
and the field of view moderately flat. Mr. Pritchard stated expressly 
of this instrument, that it was the simplest that had yet been con¬ 
structed that would accomplish all the work that might be required 
of a microscope, either for general examination, dissection, or minute 
investigation. 
Preparations of various classes of microscopic objects in Canada 
balsam were exhibited. 
Mr. Hawkins explained the principle of Saxton’s locomotive Dif¬ 
ferential Pulley; and a mode of producing rapid and uninterrupted 
travelling by means of a succession of such pulleys set in motion 
by steam-engines or by horses. 
Mr. Cheverton read a paper on Mechanical Sculpture, or the 
production of busts and other works of art by machinery, and illus¬ 
trated the subject by specimens of busts and a statue in ivory, which 
were laid on the table. This machine, in common with many others, 
produces its results only through the medium of a model to govern 
its movements; but it has this peculiarity, that the copy which it 
makes of the original is of a size reduced in any proportion, and 
that it is enabled to effect this result not merely on surfaces, such as 
bas reliefs, but in the round figures, such as busts and statues. 
Mr. Ettrick gave an account of certain improvements proposed 
by him in the Astronomical Clock for giving the pendulum a free 
motion at right angles to the line of its motion, and thereby pre¬ 
venting the tendency to acquire a circular motion by any improper 
adjustment of the pendulum-spring. 
He described a mariner’s steering-compass provided with two ad¬ 
justments, whereby the card was made to point true bearings on the 
horizon; the variation and local attraction being allowed for by regu¬ 
lating the position of the needle on the card. 
