46 Transactions of the 



the surface, and on this a sheet of cleaned pierced zinc the size of 

 the slate tablet. The blotting-pajier was damped with distilled 

 water, the piece of pierced zinc placed on it, and a sheet of clean 

 flat glass pushed along the grooves in' the elects at the two ends 

 up to the stop on the opposite side of the frame, so as to form a 

 close cover to the thin flat slate-box. When the slides had been 

 examined and memoranda made in ink on their free surfaces, they 

 were placed in this chamber, and exposed to the diffused light of 

 the room. The slate-box, holding twenty-one slides, was easily 

 managed, and the blotting-paper damped when necessary by dis- 

 tilled water from a dipping-tube, always trying to avoid adding 

 too much. 



The cultivating solution used for the thin covers and the slides 

 at the commencement varied, but preference was given to the fol- 

 lowing : — 



Thick clear treacle, 1 drachm ; 

 Saturated solution of acetate of potash, 40 minims ; 

 Distilled water, 5 drachms ; 

 boiled in a narrow covered test-tube until reduced to 4 drachms, 

 then closed whilst hot, allowed to cool and settle, a portion being 

 poured off" into a clean two-drachm stoppered bottle that had been 

 previously washed out with alcohol, and dried. 



Another solution was tried, which contained the same ingre- 

 dients, plus 6 minims of liq. Am. fort., and boiled slowly until all 

 trace of the smell of ammonia was absent. 



A clean bent needle was employed to convey enough of the 

 solution to smear the centre of the thin cover for about one-sixth of 

 an inch, and to place on the slide, when set up for cultivating, a 

 droplet of the same solution the size of a small pin head. 



1st. The position chosen for the apparatus was the supposed 

 best one the locality permitted, yet not such as to be equally ex- 

 posed to wind from every direction of the compass, being somewhat 

 protected from the S.S.W. and W. winds by the house ; and as the 

 garden is surrounded by a low wall, some diminution of the force 

 of the wind might be expected ; hence fewer particles entrapped, 

 though with every shght breeze, from any quarter, the instrument 

 revolved freely, the average height of the centre of the vane being 

 five feet. 



2nd. There appears to be no relation between a prevalence of 

 germs with the wind from any one point of the compass more than 

 another that was at all decisive, for what seemed to give such ex- 

 cess at one time was neutralized at others. 



Nor could any relation be established between the force of the 

 wind and the quantity of spores, though there was abundant proof 

 of the greater increase of dust in the air when the ground was not 

 wet. This is attributed to the light germs being carried higher 



