82 JOURNAL OF THE [January, 



besides the delicate rulings, there was much to interest the mi- 

 croscopist in the special apparatus for comparing micrometers 

 and measures. 



The stand is one constructed by Mr. Fasoldt, substituting a 

 screw movement to the body of the microscope, instead of the 

 ordinary rack and pinion. It is quick, but firm, and cannot be 

 displaced by accident and crush a ruling. 



His vertical illuminator has, like Beck's, a thin glass for a re- 

 flector. But the method of mounting, construction of the dia- 

 phragms, and means to control the light, are entirely different, 

 making it a valuable accessory. The mechanical stage is con- 

 structed for the purpose of making fine measurements, and com- 

 paring micrometers. The screw is of recent construction, loo 

 threads to the inch, carrying on one end a wheel 2^ inches in 

 diameter, and ^ inch broad, graduated with 100 spaces, each 

 0.07 of an inch long, for each tttottt) forward movement of the 

 screw. The pitch of the screw is very uniform, and enables the 

 manipulator to readily place the different bands of the ruling 

 under high power objectives; then by focussing it can be de- 

 termined whether they can be resolved. 



The eye-piece carries a delicate micrometer, which has three 

 delicate steel prongs, in lieu of cobwebs, or lines on glass. 

 Each prong is adjustable, extending part way across the field. 

 One is in the upper part, and two are in the lower part of the 

 field. The advantages of the prongs are many, one being that 

 but part of the line is covered. 



The lamp has a single wick, two inches wide. In trimming, 

 the wick is curved from edge to edge; the centre being fully yi 

 of an inch higher than the edges. The chimney is specially 

 formed of a metallic frame, carrying parallel plate-glass sides; 

 those opposite the width of the flame are about 3X4 inches, 

 and those opposite the edges are 3X2 inches. On the top of 

 the frame is put a metallic tube, about i}{ inches diameter, and 

 14 inches high, to produce the draught. The flame is large, 

 and burns very white and steady. In use the lamp is placed 

 from two to four feet from the microscope, the edge of the flame 

 being turned towards the illuminator. A small condenser, of 

 two inches focus, is placed before the illuminator, so as to throw 

 an image of the flame obliquely across the band of lines. The 

 entire field is not equally illuminated, as better results are ob' 



