1044 RECORD OF CURRENT RESEARCHES RELATING TO 



results, the diatoms mounted in it showing with " excessive beauty." 

 The strife of Ampldpleura pellucida, amongst others, were clearer than 

 he ever before saw them. Objectives, with which he had never been 

 able to see the strife by simple lamp-light, showed them at once in 

 the new medium. He considers, therefore, that its employment will 

 be found very useful wherever the delicate details of diatoms are not 

 sufficiently visible in ordinary preparations. 



Dr. L. Dippel, also writing * on Mr. Stephenson's paper, commends 

 oil of aniseed and oil of cassia for mounting, the last of which has 

 especially proved to be well adapted for making the fine structure of 

 the siliceous valves clearly visible. He has recommended both oils 

 for some years to one and another of the German mounters. Oil of 

 aniseed was employed by Professor Weiss in studying diatoms.f 



Of the fluids which Mr. Stephenson further proposes, the solution 

 of phosphorus in bisulphide of carbon is, Dr. Dippel considers, pre- 

 cluded on account of its combustibility, and mounting in bisulphide of 

 carbon as well as in the solution of sulphur is attended with so many 

 inconveniences that neither could well be taken into common use as 

 fluids for mounting. On the other hand, monobromide of naphthaline 

 is most excellently adapted for it. It does not affect wax as far as 

 experience has gone as yet, and hence objects may be conveniently pre- 

 pared with it. The cover-glass should be run round with a ring of wax, 

 then with a cement of isinglass dissolved in spirit (called Heller's 

 porcelain cement), or Canada balsam, rather thick, dissolved in chloro- 

 form ; finally closing with a solution of shellac. Amongst other 

 diatoms thus mounted, is a small and very finely striated Amphipleura 

 pellucida, the structure of which, with immersion objectives — homo- 

 geneous-immersion specially — appears wonderfully clearly and sharply 

 defined. 



Absolute Invisibility of Atoms and Molecules. J — Professor 

 A. E. Dolbear writes : — 



Maxwell gives the diameter of an atom of hydrogen to be such 

 that two millions of them in a row would measure a millimetre ; but 

 under ordinary physical conditions most atoms are combined with 

 other atoms to form molecules, and such combinations are of all 

 degrees of complexity. Thus, a molecule of water contains three 

 atoms, a molecule of alum about one hundred, while a molecule of 

 albumen contains nine hundred atoms, and there is no reason to 

 suppose albumen to be the most complex of all molecular compounds. 

 When atoms are thus combined, it is fair to assume that they are 



* «Bot. Centralbl.,' i. (1880) p. 1148. 



t Dr. Dippel, if we understand him correctly, also points out that " this 

 method of preparation is not in all respects new. He himself came upon it 

 in his investigations on the cell-wall ['Das Mikroskop,' i. pp. 67 and 83], and 

 since 1867 has mounted not only histological objects, but also various diatom 

 preparations in oil of aniseed and oil of cassia." We need hardly, however, men- 

 tion that the point of Mr. Stephenson's paper is not to describe as a noveltr^ the 

 use for mounting of phosphorus, bisulphide of carbon, &c. ; for, as he says in 

 the paper, preparations were so mounted in 1873, when his previous paper was 

 read. 

 ■ t 'Science,'!. (1880) p. 150. 



