"ounu^;/ju,[;ri«7''] Atmosi^henc Particles. 289 



The aperture of the large end of the funnel (h) may be partially 

 closed if thought proper by a ventilating fly-wheel, supported cen- 

 trally by a steel pin with sharj) ends embraced between two straps 

 of brass, fastened to the internal face of the funnel by a screw and 

 nut at about one-third of its depth from the open end ; its rota- 

 tion maj tend to increase the current when used with a lamp, 

 otherwise it is, I find, unnecessary. To use the aj)paratus verti- 

 cally, screw the extra brass tube (Fig. 4) on to (d), and slip over 

 the end of the funnel as before ; fix into the short tube on (/) the 

 gas-pipe ((/), with its small funnel attached (])), and support the whole 

 by one of the retort-holders of the laboratory, or in any convenient 

 way, and place beneath the open end of the little funnel a lighted 

 oil lamp to generate a current above the nozzle ; hence it must be 

 placed at such a distance from the apparatus as not to influence 

 materially the current through its proper course. It can be used 

 with water as an aspirator if desired, but my object has been to 

 avoid this. Its position above the surface of the ground may vary 

 from a few to many inches, according to choice. I use it at present 

 4 to 5 feet above the ground, but think 3 feet may be preferable. 

 If it be desired to test the eflicacy of various vaj)ours or fluids as 

 disinfectants or destructive of life in the germs, an extra nozzle 

 (Fig. 5, h) can be screwed on the ordinary one (/), and made as a 

 flat box having a small nozzle projecting from the cover, looking 

 towards the thin glass. If this narrow box, which should be platin- 

 ized inside, be packed with fine cotton wool, damped at one part 

 with any article, as creosote, tinct. of the muriate of iron, or solu- 

 tion of quinine, or a particle of hypochloride of hme placed at one 

 part, the particles from the air may be supposed to be entrapped 

 amongst the fibres; but the cotton-wool should, before use, be 

 soaked in absolute alcohol for half an hour, and squeezed dry 

 between heated plates of glass; or gun-cotton might be used if 

 thought more free from error. The wool from opposite the nozzle 

 might, in each case, be removed with a pair of fine scissors and 

 forceps, placed in a deep growing slide with some medium, and set 

 aside for observation. If only a cursory examination be intended 

 of the glass covers, I find a square, half an inch across, drawn on 

 the clean surface of an ordinary 3-inch x 1-inch shde, with a little 

 roll of soft beeswax, makes a very good temporary cell. Care must 

 be taken to apply only a minute quantity of the glutinous material 

 to the centre. of the thin cover. If two or three diaphragm stages (e) 

 be made, one could be screwed into place when the exposed one is 

 removed. 



It is not pretended that this form is the only useful one or the 

 most convenient that can be adopted, but as it has now been in use 

 some days, I find it answer its chief purpose very well, and is ex- 

 ceedingly easy to manipulate. The advantages claimed are, ready 



VOL. III. u 



