J. MICROSCOPES. 775 



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Small air pump for mounting. 

 Lamp for microscope, with white cloud reflector. 

 Bottles and dipping tubes for collecting materials. 

 Collecting bottle, net, hook, and jointed rod. 

 Cements, varnish, liquids, and media for mounting. 

 Boxes, cases, cabinets, for finished objects. 



Edmund Wheeler. 



36O6a. Micrographic Study of Paper Manufacture. 



M. Aime Girard, Paris. 



3607. Instrument for verifying Micrometers of Microscopes. 



W. F. R. Suringar, Ley den. 



Consists of a metallic frame, reposing at each side upon four pillars fixed in 

 a wooden bottom, through which are thrust three screws, two at the one side, 

 one at the other side, for regulating the horizontal position of the instrument. 

 Upon the frame slides another, the quick movement of which is regulated by 

 a rack and pinion, and upon this a third, destined for bearing the scale, with 

 slow motion, directed by an adjusting screw with milled head. For using the 

 instrument, put the scale, divided into a certain number (fig. 35) of millimeters 

 on the inner slide, or (in the case of microscopes with very small stage, such 

 as the small Oberhauser-microscope now shown), on the three extra supports 

 on the outer side, regulate the screws of the small additional table destined for 

 bearing the microscope, in such a manner that the stage of the microscope 

 glides under the frame, and the divisions of the scale can be centered with 

 the field of the microscope. After having adjusted the ends of the eye-piece 

 micrometer in the microscope -to the ends of the stage micrometer that is to 

 be verified, seen through the microscope, place the microscope over the middle 

 part of the instrument, move the scale till the first division of the scale can 

 be seen in the field of the microscope, adjust and measure the first division, 

 and subsequently all the others, taking care to measure always from the same 

 side (e.<7. the left) of the lines. Notice the number of entire divisions of 

 the eye-piece micrometer, and tax the tenth part of them, to which each 

 division of the scale corresponds. After having measured them all, one by 

 one, make the addition, and divide the amount by the number of divisions 

 measured. The quotient indicates the mean value of each division of the 

 scale expressed in parts of the eye-piece micrometer, viz., of the millimetre 

 of the stage micrometer. This quotient, divided into one, expresses the exact 

 value of the millimetre to be verified in parts of the scale used for comparison, 

 and itself previously compared with a standard scale. The accuracy obtained 

 is proportional to the square root of the number of divisions compared one 

 by one, and makes sure easily of the y^Vo P ar ^ f a millimetre. 



The instrument should be placed before a window, and at a distance not 

 exceeding six feet from it, because otherwise the scale would not receive 

 sufficient light for seeing the divisions clearly through the microscope. 



A description of verifications made by the instrument, with cut, accom- 

 panies it. 



3608. Apparatus for Microscopical Research in the 



open air. Prf> Dr. Leonard Roesler, Klosterneuburg . 



3609. He-agents for Micro chemical Researches, in box. 



Prof. Dr. Leonard Roesler, Klosterneuburg. 



