528 
POPULAE SCIENCE REVIEW. 
to be a most valuable addition to our list of appliances. It is composed of 
three parts : — first, a piece of horn of the shape of the mouth when open, 
pierced by two holes. (2.) Two india-rubber tubes communicating with these 
holes ; and (3rd.) a nose-pincher, which prevents respiration through the 
nostril. The pincher being applied to the nose, the mouthpiece is held in the 
mouth by pressure of teeth, and the workman can then, by closing the ex- 
piratory hole with his tongue, draw in air through one tube, and then by 
placing his tongue upon the second hole he can breathe out foul air through 
the other tube. A second form of this invention differs from the first, in 
having the tubes communicatmg with a reservoir upon the workman’s back- 
This is intended for the use of firemen and others who have, for a short period, 
to enter an atmosphere of foul air or smoke. The inventor also employs 
peculiar glasses for the protection of the eyes. This apparatus may be seen 
at the Polytechnic Institution. 
MICEOSCOPY. 
A Graduating Diaphragm . — A very ingenious diaphragm has just been 
devised by Mr. CoUms, of Great Titchfield Street. The advantages of the new 
instrument can only be appreciated by those who understand the necessity 
which exists for regulatmg the amount of light which is reflected from the 
mirror of the microscope upon the object mider investigation. In the ordi- 
nary ‘‘ wheel of diaphragms ” there are about half a dozen apertures of 
different sizes, and the observer rotates the disk untO. he finds an aperture 
which admits the proper flood of light. There are, however, two serious 
objections to this method : — 1st. As the number of holes is limited, the 
microscopist, though enabled to select the best aperture of the series for his 
purpose, may not be supplied with such an aperture as would give the exact 
absolute degree of illumination. 2nd. While rotating the “ wheel ” to obtain 
the required result he loses sight of his object, and thus is unable to perceive 
fully the advantage he has derived from the alteration. Both these disad- 
vantages have been overcome in Mr. Collins’ diaphragm, which provides a 
means by which any sized aperture may be obtained without removing the 
object from observation. The subjoined engraving explains the apparatus. 
It consists of a plate, placed beneath the stage, and having below it two 
smaller ones, whose opposite sides are incised in a cuneate manner, and 
which, when separated, leave a large lozenge-shaped aperture ; but, when 
caused to approach, gradually diminish this aperture tiU. it is reduced to a 
mere point. The approximation and separation are effected by means of a 
screw, whose mdled head is within easy reach of the observer’s tinger. This 
piece of apparatus may easily be appended to any microscope, and the man- 
ner in which it aids in the display of the striae of enamel and muscular fibre, 
and the delicate markings of the diatomaceae, must be seen to be fully appre- 
ciated. Obviously its greatest merit lies in the power which it gives to the 
observer of graduating his aperture of illumination with the greatest nicety, 
and of estimating the improvement in the definition of fine points of struc- 
