866 SUMMABY OF CURRENT RESEARCHES RELATING TO 



electric light is really now brought to every one's door, and we cannot 

 too strongly advise microscopists, especially diatomists, to whom the 

 electric light is indispensable, to provide themselves with one of these 

 apparatuses, the price of which is very moderate. An experience of 

 more than three years has shown us that when the electric light has 

 been once tried and the really marvellous facility noted with which it 

 resolves at the very outset the most difficult details of structure, it 

 cannot be given up again, and the expensive lamps with which we 

 were so recently content are thrown aside." 



Illumination for Projection Microscopes.* — M. d'Arsonval de- 

 scribes an improvement in the illumination of projection apparatus by 

 the employment of a petroleum lamp with three burners, of which 

 the middle one heated by the two lateral ones " allows of an enormous 

 intensity of light, augmented moreover by a reflector at the back." 

 In addition to the fact that this apparatus gives an illumination 

 nearly equal to that of the largest projection apparatus, it is much 

 less costly. The use of napthalin increases still more the light and 

 favourably modifies its nature. 



MM. Malassez and Henocque lay stress on "the enormous 

 advantage to be obtained from naphthalin, which gives a white light, 

 very useful for microscopical or spectroscopical examinations." 



Lantern Transparencies.! — Mr. C. M. Yoree says that where a 

 considerable number of lantern slides are desired, as for distribution 

 among co-workers, they can be made considerably cheaper by the use 

 of the carbon process than by using dry plates. The process' is very 

 cheap and not difficult of application ; for the author's description of 

 it the original must be referred to. 



Lantern transparencies when prepared to show microscopic objects 

 very highly magnified are best made from camera enlargements of a 

 less highly magnified negative, as follows: — Prepare a negative 

 showing the desired points by means of an objective of as low power 

 as will clearly show all the desired details. This negative will be 

 smaller than is required, but will be a better one than one made of 

 the desired size by a higher power, because the penetration of the 

 objective will give sharper projection than if a higher power were 

 used. Place the negative in a copying camera and enlarge it to the 

 desired size if possible ; if not, a second enlargement would be re- 

 quired, but is seldom if ever necessary. The second plate, that is, 

 the enlargement of the first negative, is a positive, and if well done 

 may be moimted as a lantern slide ; but first a negative is made from 

 this by contact printing, and from this negative not only paper prints 

 but other lantern positives may be made at will. It should be noted 

 that if any retouching in the original negative is required it must be 

 done with care and skill, as any errors would be exaggerated by the 

 enlargement, but the enlarged positive may be freely retouched before 

 being used for contact printing, and thus letters, figures, names, &c., 



* Journ. Soc. Scientifiques, i. (1885) p. 140. (Soc. de Biologie, 1885, March 

 21st.) 



t Amer. Mon. Micr. Journ., vi. (1885) pp. 84-5. 



