554 



Progress in Science. 



[Oaober, 



wards, and these cylinders by compression take naturally the hexagonal form, 

 so that according to the part focussed, and the nature of the illumination 

 employed, dots, lines, hexagons, or beads may be seen. 



Mr. Sorby makes a valuable communication to the " Monthly Microscopical 

 Journal " for July on the " Spectrum Method of Detecting Blood." After 

 describing the best combination of prisms to be employed in the spectrum- 

 microscope, which are recommended to be of moderate dispersive power, 

 and the cells, and other apparatus and reagents useful in these exami- 

 nations, he proceeds to demonstrate the characteristics of the blood spectrum, 

 and the changes caused in it by the action of reagents. The changes caused 

 by exposure to damp are next noticed, and valuable information is given 

 respecting the detection of old blood-stains. The action of mordants and 

 dyes in fabrics, and the variations in manipulation caused by their presence, 

 are duly treated upon, and the recognition of blood in very diluted solutions 

 is shown to be possible. The whole paper is of great interest to all workers 

 with the micro-spectroscope and those engaged in medico-legal enquiries. 



Mr. Ladd has contrived a polariscope to be used with the microscope in 

 the examination of the rings about the optic axes of crystals, which has the 

 advantage of being less expensive than ordinary appliances for the purpose, 

 and also gives so large a field that both the axes of sugar are easily brought 

 into view. Beneath the stage is placed a pair of lenses somewhat resembling 

 an ordinary Huyghenian eye-piece, but with a nearly hemispherical front 

 glass ; this acts as a condenser. A similar combination of lenses is attached 

 to the body of the microscope in the place of the objective; a double convex 

 lens is placed in the bottom of the draw-tube, which is here used for the 

 purpose of focussing; beneath the condenser is placed the ordinary Nicol 

 prism, and a low power eye-piece with a Nicol prism above it as an analyser 

 completes the arrangemet. 



HEAT. 



In the phenomenon of the spheroidal state, the globule will float when the 



vapour beneath it is able to support the pressure of the atmosphere plus the 



weight of the globule. If we remove the former factor, a much smaller 



vapour tension will be required to produce the phenomenon, as may be proved 



by the following experiment, de- 

 Fig. ig. scribed by E. Budde, in which, 



with the aid of the air-pump, a 

 Liedenfrost globule is supported 

 upon a metal plate whose tem- 

 perature is below ioo° C. A bell- 

 shaped glass vessel, g, is firmly 

 cemented to a copper plate, a. 

 Through the stopper which closed 

 the upper opening pass two glass 

 tubes, /and m. The first attaches 

 by caoutchouc tubing to the air- 

 pump. The second reaches within 

 the vessel nearly to the plate a, 

 while above it is closed and bent 

 into an N form. The bent por- 

 tion is filled with water. The 

 plate is now placed upon the 

 water-bath, which soon imparts 

 to it a temperature of from 8o° to 

 ioo° C. The air-pump is now put 

 in operation ; the water in N 

 evolves air-bubble and vapours 

 (gentle heating will facilitate the 

 operation), which mainly accumu- 

 late in the upperend of the tube — 

 The water falls boiling, or very 



i \ 

 1 ■' / ! 





1 

 1 



j 



— SV.. M 



1 





i 



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1 



and force a portion of the water through 



