276 



Progress in Sciencg. 



[April, 



portability, the size of the cylindrical case, Fig. ig, in which it is packed 

 being only 6 inches by 3 inches, and its disposition when put away will readily 

 be understood by Fig. 20. The chimney is of metal, and to enable it to be 

 placed in so small a case, the upper part consists of two joints sliding into each 

 other like the drawers of a telescope ; the aperture in the bulb is furnished with 

 white and tinted glasses, and also with a plano-convex lens for obtaining 

 parallel rays. The general form of the lamp is shown in Fig. 21. An arrange- 

 ment is made which permits the lamp to be tilted to a slight extent when 



Fig 



Fig. ig. 



Fig. 20. 



required. The burner is small and of good quality, and the intensity of the 

 light much increased by the white lining of the interior of the chimney, which 

 can easily be renewed whenever it becomes discoloured by the deposition of 

 soot. Mr. Browning is engaged in making provision against the liability of 

 spilling the paraffin in case of the accidental inversion of the lamp during con- 

 veyance from place to place, an improvement that will be fully appreciated 

 by microscopists who are in the habit of using their instruments away from 

 home. 



Captain F. H. Lang, President of the Reading Microscopical Society, com- 

 municates his experience, and that of Captain Haig and Mr. Tatem, respecting 

 the selection and mounting of diatoms. The instrument preferred by Captain 

 Lang for picking up diatoms is a finely pointed badger-hair, whipped on to a 

 light handle, so that the hair does not project more than about fths of an inch. 

 This is dipped into a weak solution of gum and allowed to dry, and, when 

 breathed upon, the most delicate form from a dried gathering may be taken up, 

 and will remain on the hair whilst the slide containing the general gathering is 

 shifted, and that on which it is to be placed substituted. Captain Haig uses a 

 thin cell, formed of gold-size, baked until it is partially carbonised after the 

 manner of japanning, to prevent the diatoms being crushed by pressure. The 

 diatoms are to be mounted on the cover in preference to the slide, on which is 

 placed a smear of glycerine, containing a minute quantity of gum to keep the 

 diatoms in their places. The glycerine is then disposed of by evaporation on a hot 

 plate, and the diatoms mounted either dry or in balsam, or the solution of balsam 

 in benzol or chloroform. Mr. Tatem places his cover, on which the diatoms have 

 been arranged, on the cell which has been filled with chloroform, and places a 

 drop of balsam in contact with the edge of the cover, allowing it to run in as 

 the chloroform evaporates. For keeping the diatoms in their places when gum 

 is necessary, a grain and a half in an ounce of distilled water is generally suffi- 



