0U2 SUMMARY OF CURRENT RESEARCHES RELATING TO 



source of the illumination ; in fact, they would exhibit the same 

 appearances as those presented by the eye of a beetle when viewed 

 microscopically. From this we may assume that when the markings 

 on diatoms are exactly at right angles, the most perfect lenticular 

 performance would bo visible. 



A very pretty microscopic object may be produced in the follow- 

 ing manner : — Place a metal ring on a slip of glass ; in the centre of 

 the metal ring put a minute quantity of the flowers of sulphur, and 

 place a thin cover-glass over the metal ring ; then hold the strip of 

 glass at some distance above the flame of a spirit-lamp, in order to 

 sublime the sulphur; when the slip of glass is placed under the 

 Microscope, and viewed with a moderately low power, the sublimed 

 sulphur will ajipcar as minute plano-convex lenses, in which the 

 image of an object placed between the mirror and the source of light 

 will be beautifully shown. These piano lenses will remain trans- 

 parent so long as the cover-glass is kept moderately warm. When 

 cooling, the act of crystallization may be observed ; when cold, these 

 minute hemispheres are opaque. It may be necessary to repeat the 

 experiment to insure the best results. If too much sulphur, or too 

 much heat, the lenses are not microscopic. By blowing through a 

 heated glass tube, on to the surface of the cover-glass, the act of 

 crystallization can be retarded." 



« Central v. Oblique Light."— Mr. E. M. Nelson thinks* that he 

 has been hardly dealt with by the " Royal Microscopical Society," f 

 who in place of meeting his " criticisms en their teaching " in a 

 proper scientific spirit, have made a " personal attack " upon him 

 and are threatening him with their sledge-hammer. This is the 

 story of the wolf and the lamb in an intensified form. 



How criticism should be met depends upon circumstances, and 

 there are occasions when " personal attack " (adopting Mr. Nelson's 

 term) is the only remedy, except silence, which is open to the 

 aggrieved party. 



Suppose Mr. Nelson had, for instance, published a statement ex- 

 pressive of his regret that Prof. Huxley was so determined an opponent 

 of Darwinism, and that, in consequence, he intended to demonstrate 

 the falsity of the Professor's teaching. Does he suppose that Professor 

 Huxley would proceed to discuss the matter in a " proper scientific 

 spirit," or that if in place of treating it with silent contempt (as he 

 probably would) he made a " personal attack " by way of reply, would 

 any one consider it as otherwise than well-deserved ? 



But Mr. Nelson has gone much further even than the case we 

 have put. When he first misrepresented the " Eoyal Microscopical 

 Society " as teaching the views which he combated, we pointed out 

 that not only were those views not held as suggested, but that we had 

 never met or heard of any one who holds or had ever held them. In 

 decent society it is usual, when a person has disclaimed an opinion 

 improperly attributed to him, to do one of two things — either to with- 

 draw it (with or without an expression of regret at having made it, 



* Engl. Mech., xliii. (1S86) p. 300. t See note s'ipra, p. 574. 



