INVERTEBRATA. CRYPTOGAMIA, MICROSCOPY, ETC. 849 



point of view. It is, however, to tbe biologist that we must look 

 chiefly for the future elucidation of the subject, and he has a field of 

 the widest range, embracing much untrodden ground, for his investi- 

 gations. 



Browuian Movement. — ^Similar motions to those shown under the 

 Microscope by small particles in liquids have been attributed to dust- 

 particles in air, and accounted for by the shock of molecules with the 

 particles. 



In a paper treating fully of the movements of very minute bodies,* 

 Herr Niigeli calculates (from data of the mechanical theory of gases 

 as to the weight and number, and collisions of molecules) the velocity 

 of the smallest fungus-particles in the air that can be perceived with 

 the best instrument, supposing a nitrogen or oxygen molecule to drive 

 against them. It is, at the most, as much as the velocity of the hour- 

 hand of a watch, since these fungi are 300 million times heavier 

 than a nitrogen or oxygen molecule. The ordinary motes would 

 move 50 million times slower than the hour-hand of a watch. Numbers 

 of the same magnitude are obtained for movements of small jiarticles 

 in liquids. In both cases a summation of the shocks of different 

 molecules is not admissible, as the movements ai'c equally distributed 

 in all directions. 



Niigeli therefore disputes the dancing motion of solar dust-particles, 

 and attributes the Browniau molecular motion to forces active between 

 the surface molecules of the liquid and the small particles ; but he 

 does not say how he conceives of this action.f 



Examining very soft Rocks. — The following process of preparing 

 sections of very soft and friable rocks is communicated J by Mr. J. A. 

 Phillips to Mr. F. Rutley. The chip, which may be to some extent 

 hardened by saturation in a mixture of balsam and benzol until 

 thoroughly impregnated with it, and afterwards dried, should be 

 gently ground or filed down until a smooth, even surface is i)rocured ; 

 this surface must then be attached to a piece of glass slide cut about 

 an inch square, and this again fixed in a similar manner by old balsam 

 to a thicker piece of glass if needful, so that it can be conveniently 

 lield whilst the grinding is carried on. When it is reduced to such a 

 degree of tenuity that it will bear no more grinding, even with the finest 

 materials, such as jewellers' rouge, and when the removal of the section 

 from the glass to which it is attached would almost inevitably result 

 in the destruction of the preparation, the lower i)iece of glass should 

 be warmed and separated fi'om tlic ujjper jjiecc wliich bears the section, 

 and this, with its attached section, should be again cemented by the 

 under side of the glass to an ordinary glass slip, covered in the usual 

 way, and if the edges of the section, or its glass, be disfigured by 

 grinding, a ring or square margin of lh-uns\vick black or asphalt may 

 be painted over the unsightly j)iirt. 



* 'SB. K. Bay. Akad. Wi.s.^.,' ISTD. p. HSO. 

 t Sfu ' Natuiv,' xxi. (ISSii) |>. :i.")L». 



I V. Hiitl.y'.-, 'Stii'ly <>( UcM-k, ' (Sv,,. London. 1S7'.»). |' 70. 

 VOL. III. 3 K 



