Journal of Applied Microscopy. 551 



microscopes are not usually arranged for changing quickly from plain to polar- 

 ized light, and vice versa. Usually the polarizer is fitted to the substage 

 ring, which carries the Abbe condenser and cannot be attached until the sub- 

 stage is lowered and the condenser is removed. For attaching the analyzer the 

 microscope tube must be raised, the objective or nose-piece removed, and the 

 analyzer screwed at the upper end to the tube, and at the lower end to the 

 objective or nose-piece. Both the substage and the tube must be readjusted 

 before the object can be viewed. The change back again to plain illumination 

 is equally laborious. These operations not only consume several minutes each 

 time the polariscope is brought into service, but also, if often repeated, are 

 ruinous to the screw threads and other parts of the apparatus. 



In Fig. 1 is shown a Bausch & Lomb Continental microscope fitted with an 

 arrangement devised by the writer, which obviates all the disadvantages which 

 have been named. The polarizer (Fig. 2) is carried on an arm below the 

 substage, and swings into position from the right, at the same time forcing the 

 iris diaphragm out of posi- 

 tion to the left. The ana- 

 lyzer is mounted in the 

 same manner as in petro- 

 graphical instruments, the 

 prism being contained in a 

 box which slides in the 

 main tube, so that when 

 pushed to the right the light 

 passes through the prism, 



but when pushed to the left, "^^H^P^ "^ -vZ^";^.' 



a round opening permits F'g- -• 



unobstructed vision. 



When polarized light is desired, the polarizer is pushed to the left, and the 

 analyzer box to the right, and the change to plain illumination is accomplished 

 by the reverse operations. Either change can be made in less than a second, 

 without disturbing the adjustment either of the tube or the substage, and without 

 damage to the instrument. 



Another advantage is that the condenser may be used in conjunction with 

 the polarizer, thus rendering the crosses on wheat, rj^e, barley, and some 

 other feebly active starches much more distinct. 



Selenite plates are mounted in a metal slip and are used on the stage. 



Now that the microscopic examination of food products is coming into 

 importance in the United States, the question arises as to the form of microscope 

 best adapted for this work. 



After experience with several types of instruments, the writer prefers a Con- 

 tinental stand, provided with two-thirds and one-sixth-inch objectives, double 

 nose-piece, one and two-inch oculars, micrometer mounted in extra one-inch 

 ocular, mechanical stage, iris diaphragm. Abbe condenser, and the polarizing 

 apparatus which has been described. 



A microscope of this description (Fig. 1) has been in constant use at this 

 station for several years and has been found to fully meet the somewhat peculiar 

 requirements of the food analyst. A. L. Winton. 



Connecticut Agricultural Experiment Station. 



