914 SEC. 18. BIOLOGY. 



This instrument, of which the general construction is that of Ross' English 

 microscopes, has the following arrangements : It may be used in different 

 positions, vertical, horizontal, or oblique, and is specially applicable to the 

 photography of microscopic objects. The illumination is effected by means 

 of a mirror carried by a system of jointed rods, which limits its movement to 

 an arc, the centre of which is the object to be observed. The best illumination 

 is thus quickly secured, the observer not having tc regulate at the same 

 time the focal distance of the mirror and its lateral distance from the axis 

 of the microscope. The condenser is moved by means of a rack, which serves 

 to regulate exactly the position of the diaphragm. The whole condensing 

 system, turning around an eccentric axis, can be very rapidly modified. 



The stage turns independently of the tube. The focussing is effected, for 

 coarse adjustment, by means of a rack, and for fine adjustment by means of 

 a milled screw acting upon the tube supporting the objective, by the inter- 

 vention of a lever that lessens the amplitude of the movement. 



The tube supporting the objective is carried by a spring which serves to 

 prevent the objects being crushed, when by mishap the objective is lowered 

 too quickly. The milled screw for focussing is used as well for the micro- 

 metrical measurement of objects under observation as for focussing in the 

 use of the objective in photography. 



The objective is not screwed on to the tube, it is only pressed by spring 

 clips against a steel bearing adjusted with the greatest care. To take off 

 the objective, it is sufficient to draw it away transversely by pressing in the 

 direction of the tube of the microscope. The objective is fixed as instan- 

 taneously as it is removed. The advantages resulting from these arrange- 

 ments are the following : 1st. A great saving of time to the observer. 2nd. A 

 mechanical centring of the objective much more perfect than that obtained* 

 by a screw. The defects of centring being immediately discovered may be 

 partly corrected. 3rd. There is the easy choice of the side of the objective 

 that gives the best effect when the oblique illumination is employed. 



3582. Microscope, with durable body, with rotating move- 

 ment round its axis, fine adjustment by means of steel prism, 

 condenser, polarising apparatus, magnifying power from 10 to 

 1,200 diameters. W. TescJiner (successor to Amuel), Berlin. 



3583. Microscope, with magnifying power from 20 to 1,000. 



W. Tesckner, Berlin. 



35S7. Polarising Microscope, with movable body and 

 prism. M. A. Picort, Paris. 



3 5 S3. Polarising Microscope, with movable body. 



M. A. Picort, Paris. 



3539. Picort Vertical Polarising Microscope. 



M. A. Picon, Paris. 



3589a. Polarising Microscope, with lens for parallel light, 

 and Nicol prisms for measuring the axes. Laurent, Paris. 



The illuminating part which is used in the case of crystals of one and of 

 two axes, that is to say, for converging light, can be removed by hand and 

 replaced by a lens set in a ring ; the whole objective part is also removed, 

 and the apparatus is then used for parallel light. There is, moreover, the 

 movable eyepiece for the sighting, and the flat tints are very uniform and 



