THE SWIFT. — IMPROVEMENT IN THE MICROSCOPE. 199 



these little creatures, but have not observed any since that 

 date.— T. Bell Salter.— Ryde, March 15th, 1839. 



Note on the Hirundinidce. — On Wednesday, July the 25th, 

 1838, about a mile from Blackburn, I saw an immense multi- 

 tude of swifts {Cypselus Apus) ; there were several himdreds 

 of them : the locality was a print- work and a factory, turned 

 by a water-wheel, a large lodge of water, and several streams, 

 close by the river Darwen ; this is always a favourite haunt 

 of the whole of the swallow tribe, and they are generally met 

 with there in great numbers, but so large an assemblage of 

 swifts I never saw before, for of late years there have been 

 very few of them. Could they, at that early period be pre- 

 paring for their annual migration ? 



On Friday, October 19th, 1838, I saw three swallows ho- 

 vering in the streets of Blackburn ; they were busy hawking 

 for flies, were strong on the wing, and apparently adult birds. 

 — John Skaife. — Blackburn, Oct. 2\st, 1838. 



Improvements in the Microscope. — In the ' Magazine of 

 Natural History' for June, 1838, page 345, was inserted a no- 

 tice of improvements in the microscope, made by myself. I 

 have now to inform you of an additional improvement for 

 equalizing the light, and of a facility in adjusting the focus, 

 which now scarcely leaves anything to be wished, in the use 

 of this most invaluable instrument of research in its improved 

 state. 



To equalize the light, I have mounted upon the top of my 

 graduating tube, an exceedingly finely greyed plate of glass, 

 and by this means produce the effect, so very desirable, of a 

 cloud. I thus entirely get rid of the unpleasant glare and 

 glitter produced by the use of a candle or lamp. The greying 

 effect was produced on the surface of the glass plate by the 

 employment of emery, which was suspended in water half a 

 minute, and was thus levigated in a very high degree indeed. 



The adjustment of the focus, so highly necessary to accom- 

 pany every change in the position of an object, 1 now effect 

 as follows. I have before stated that Mr. Andrew Ross had 

 effected the minute adjustment of the focus, by a fine screw 

 with a milled head. Now, this milled head is placed upon 

 the top of the stem of the microscope, and I had only to bring 

 the left hand into use, instead of letting it lie idle as usual, 

 and to employ it to turn the milled screw-head ; and I thus 

 at once constantly effected the minute adjustment of the focus 

 with every change in the position of the object. 



I hardly need expatiate upon this great advantage in the 

 use of the microscope. The right hand is fully employed in 

 effecting the crossing motions of the stage ; and thus both 



