1893.] MICROSCOPICAL JOUllNAL. li:^ 



water ctVcctually aiul economically by a combination of heat and 

 pressure. As described in the Journ. dc Micrugr , xvi. pp. 

 145-52, it consists of four ilistinct parts— a boiler, primary and 

 secondary converter (or cooler) , and a clarifier. The water to 

 be sterilized is introiluced into the primary converter — a cylindri- 

 cal metal vessel surrounded bv a worm in which water heated to 

 i20''-i3o', and just cominj^ from the boiler, is circulatinjj. P'rom 

 the converter, and havin*^ been raised to 100°, the water is con- 

 ducted alonji; a pipe to a worm nmninj; around the boiler, where 

 it is heated up to 120^-130". From tliis worm the water then 

 passes throui^h the worm in the primarv converter, thence through 

 the secondary converter, and fmally, having passed through 

 the clarifier, completes its circuit. The secondary converter is 

 also a worm surrounded liy cold water, and might be termed the 

 cooler. The clarifier is filled with powdered silica, apparently 

 between lavers of canvas, and is not intended for a filter, but to 

 impart a clearness or limpidilv to the water which has been re- 

 moved from it bv the heating it has gone through. The water 

 having passed through the clarifier is delivered bright and clear 

 and fit for all the purposes of life. 



To compute the magnification of an object photo- 

 graphed with or without an eyepiece and at different 

 distances from the objective. Tiie easiest way to find this 

 magnification is to remove the object after photographing it. 

 Put a stage micrometer in its place, throw the image of the 

 lines on the ground glass and compare them with an ordinary 

 rule. This will give the correct magnification produced by that 

 optical combination. To compute it more or less accuratelv, 

 reckon that an inch objective will amplifv 10 diameters at 10 

 inches from its optical centre. If an inch eyepiece is used mul- 

 tiply again by 10. Other objectives, eyepieces, and distances 

 in proportion. 



X' , , r , . D O .^ . ^ r , • 



Aelson s tormula is , ,, magnihcation, A = rocal rating 

 A B ^ * 



of eyepiece. B = focus of objective, O = optical tube length 



(from optical centres), D distances from object to eye or 



ground glass. As eyepieces and objectives are rarely rated cor- 



rectlv. computation bv anv; rule will gi^•e approximate results 



onlv. 



killing Nematodes for the Microtome. — Mr. C. W. Stiles, 



Annric.Tn Xatiiralist 'yi8gz) recomnicnds tlie following method : 



Onlv one worm can be killed at a time ; place it on a large 



slide with a few drops of water ; place a second slide over the 



worm and move it slowly to and fro. This movement causes 



the worm to straighten. As soon as the Nematode assumes the 



desired position pipette in the fixing solution between the slides, 



continuing the motion of the upper slide until the worm is dead. 



By this method a specimen can be obtained which is perfectly 



straight and sound. Pressure on the delicate worm mav be 



