BAIRD &IATLOCK (LONDON) LTD. 



1350 1351-1355 



1350' Filar Micrometer (Bausch & Lomb's) . . . . . . . . . . ..4100 



This micrometer, which is intended for the most accurate measurements, is constructed after the same general 

 plan that we use in the micrometers for our surveying and astronomical instruments. 



A micrometer screw acts on a slide that carries the movable wire. One revolution of this screw moves the 

 wire 0.5 mm. across the field. This screw has a drum head divided into 50 parts, one part, therefore, being equal to 

 o.oi mm. One tenth of this interval (equal to o.ooi mm. i p) can easily be estimated. A fine line running 

 through the centre of the field, parallel to the axis of the screw, serves as a guide in orienting the object with 

 reference to the direction of motion of the movable wire. 



A glass scale placed in the field and ruled in intervals of 0.5 mm. each serves for counting the full revolutions 

 of this screw. Every second interval of the scale is numbered. The eyepiece, which can be focussed on the move- 

 able wire and scale, is of the Ramsden type and has an equivalent focus of 20 mm. (12.5 x ). 



The Filar Micrometer may be attached to any microscope. It fits into the draw tube and is secured by a set- 

 screw, shown at the left in the illustration. When ordering, the exact inside diameter of the draw tube should 

 always be given. The instrument is finished in black in all exposed parts, except the screw heads, and is supplied 

 in a velvet-lined morocco case. 



Bausch & Lomb's Drawing Apparatus. 



This will be found a very useful accessory in all departments of biological work. It is designed for drawing 

 from microscopic specimens where magnified images of from 50 to 430 diameters are desired, the full diameter of 

 the image circle being utilized for all magnifications within that range. It enables one to work with the eye at its 

 normal reading distance from the pencil, a feature greatly appreciated by anyone doing much work of this character. 

 The apparatus is very simply but accurately constructed and is thoroughly satisfactory in use. Adjustments 

 are reduced to a minimum, the standard image distance of 250 mm. (10 in.) from mirror to drawing surface being 

 fixed. While illustrated with a microscope, it is not so furnished unless specified, as it is designed to accommodate 

 almost any standard instrument. 



SPECIFICATIONS. 



Microscope Support. Of wood, substantially constructed and neatly finished ; permanently attached to base 

 which is one piece with drawing board ; top surface 128 by 175 mm., height 90 mm. .assuring standard image 

 distance of 250 mm. with microscope in position ; provided with simple metal clamp to hold microscope rigidly 

 in place. 



Drawing Board. Provides smoothly finished drawing surface 282 mm. (nj in.) square with light shield in 

 position. 



Light Shield. Sheet metal, neatly finished in black to avoid reflections ; of a size and form to shade effectively 

 three sides of the drawing surface. 



Mirror. 50 mm. in diameter ; hinged, with stop at angle of 45 to direct image perpendicularly to drawing 

 surface ; mounted on metal clamp which can be readily attached to microscope draw tube in any desired position ; 

 mirror can be raised for changing eyepieces without removing. 



Lamp. Special hand-feed 90 arc, protected by metal hood having small observation window ; provided with 

 bull's-eye condenser, adjustable in tube for giving parallel or converging beam of light as desired ; entire lamp 

 mounted on support and adjustable vertically and laterally. 



Rheostat. Of fixed form, accommodating no volts, 5 amperes of current ; must be used with arc lamp to regulate 

 the current 



135 1 1 Complete Drawing Apparatus, as described, without microscope .. .. .. 550 



1352 T Drawing Board, with microscope support and clamp, and light shield .. .. 14 6 



1353 T Mirror, complete with clamp .. .. .. .. .. .. .. 10 6 



1354 T Special Hand-Feed 90 Arc Lamp, with bull's-eye condenser, as described (requires 



rheostat also) . . . . . . . . . . . . . . . . ..300 



1355' Rheostat, fixed form, no volts, 5 amperes . . . . . . . . 1 10 



Note. Please specify voltage of wiring when ordering. 



ICHEMICAL AND SCIENTIFIC APPARATUS AND PURE CHEMICALS. 



