HAKDWICKE'S SCIENCE-GOSSIP. 



15 



semi-opaque objects the green is very effective, and 

 adds materially to the stereoscopic effect when the 

 binocular is used. Tiie same sized well that is 

 used with a two-inch will work with any objective 

 up to a two-thirds. Another advantage connected 

 ■with the revolving wells is the facility with which 

 an object can be examined by transmitted light. A 

 word or two on the management of the Lieberkuhn : 

 This very useful adjunct has of late years been 

 somewhat neglected for other methods of illumina- 

 tion. My experience (over twenty years) leads me 

 to prefer it to any other kind of apparatus ; the 

 glare produced by it, and of which many microsco- 

 pists complain, may be got rid of by throwing 

 the mirror out of the centre, and thus throwing up an 

 oblique pencil of light ; the object will then have a 

 brighter beam of light on one side than the other, 

 and elevations or depressions will come out with 

 great distinctness. — F. Kitton. 



Dyeing Wood Sections.— I hope that one of 

 the following solutions will suit " J. E,." Dr. 

 Beale's carmine solution : " Carmine, 10 grains ; 

 strong liquor ammonia, half drachm ; Price's gly- 

 cerine, 2 oz. ; distilled water, 2 oz. ; alcohol, 

 \ oz. The carmine, in small fragments, is to be 

 placed in a test tube, and the ammonia added to it. 

 By agitation, and with the aid of the heat of a 

 spirit-lamp, the carmine is soon dissolved. The 

 ammoniacal solution is then to be boiled for a few 

 seconds, and allowed to cool. After the lapse of an 

 hour, much of the excess of ammonia will have 

 escaped. The glycerine and water may then be 

 added, and the whole passed through a filter." 

 Thiersch's fluid is composed of two solutions : 

 No. 1. Carmine, 1 part ; caustic ammonia, 1 part ; 

 distilled water, 3 parts. No. 2. Oxalic acid, 1 part ; 

 distilled water, 23 parts. These solutions to be 

 mixed in the proportion of 1 to S. When thoroughly 

 mixed, add absolute alcohol 12 parts; allow the 

 whole mixture to stand four or five hours, and then 

 filter. Thiersch's lilac-colouring solution is com- 

 posed as follows : Carmine, 1 part ; borax, 4 parts ; 

 distilled water, 56 parts. " The red solution is to 

 be mixed with twice its volume of absolute alcohol 

 and filtered. The precipitate of carmine and borax 

 is re- dissolved in distilled water, and is ready for 

 use." The sections to be dyed should be placed in 

 a watch-glass, with a few drops of one of the 

 solutions for a day or two, when they should be 

 carefully washed in distilled water, and are then 

 ready for mounting. — T. C. T. Walrond. 



Bunt op Wheat as a Lens. — " A. M., Paris," 

 may show the image in any beetle's eye that is well 

 mounted as a transparent object. If he does not 

 possess one, he should select a beetle whose eyes 

 have large ocelli, and macerate its head in water or 

 liqmr potassce, until the membrane bearing the 



corneules can be easily removed. This should be 

 well washed in pure water, cleaned with a camel- 

 hair pencil, and dried between two slips of glass 

 under pressure. Even in this dry state the lenses 

 will show the image ; but it is better to mount the 

 eye in Canada balsam, which, by lengthening the 

 focus of the lenses, increases the size of the 

 image. The eyes of almost any insect treated ia 

 this manner will show the image more or less 

 perfectly. The ocelli of the cicadidce being large, 

 are well adapted for the experiment, but the eyes 

 of the coleoptera are, perhaps, the most easily 

 managed, and most certain in action. To show the 

 image, the slide containing the mounted eye or the 

 bunt of wheat, should be placed on the stage of the 

 microscope, and focussed with an objective of about 

 |-inch focal length. A. small object having a 

 well-defined outline should then be moved about 

 between the stage of the microscope and the 

 source of illumination, until its shadow is seen 

 dimly through the lenses. It may then be brought 

 sharply into focus by moving the objective away 

 from the slide if the insect's eye be used, or towards 

 it for the bunt of wheat. The effect is much im- 

 proved if an achromatic condenser be used below 

 the stage, or an objective of low power may be 

 substituted for the condenser. Some microscopists 

 fasten underneath the stage a blackened pasteboard 

 tube, having at its further end an arrangement for 

 holding glass slides, on which various designs have 

 been drawn or photographed. A portrait thus 

 shown is interesting from its stereoscopic appear- 

 ance, as well as from the number of times it is 

 repeated. Sometimes a hole is cut in the side of 

 this tube to admit of a strong light being condensed 

 on an opaque object, which is also well shown by 

 the lenses. If " A. M." still finds any difficulty, I 

 shall be glad to send him a slide or two, and any 

 further particulars he may require. — F. W. M. 



Bone-dust in Soap. — Those of our readers who 

 have experienced an irritating effect in the skin 

 after the use of old brown Windsor soap, can, by 

 applying the microscope to the soap, detect the 

 presence of fine particles of gi'ound bone, which 

 have not been separated from the fat of which the 

 soap was made. These particles are abundant in 

 the cheaper kinds of soap. 



Monochkomatic Sunlight.— Mr. J. E. Smith, 

 of Ohio, has obtained light with which he is perfectly 

 satisfied by means of a light sky-blue and dark 

 green glasses. He prefers to use one blue glass 

 combined with two or three green ones, the best 

 shades being ascertained by trial. Several such 

 sets, of different depths of colour, may be mounted 

 in a series, like magic-lantern pictures, so that 

 either set can be brought easily over the hole in the 

 shutter. By sunlight transmitted through a com 



