100 Mr. Thom on New Self-acting Sluices. 



consisting of a brass rim raised upon the circular plate of 

 brass AB, and its position shifted till the black processes, seen 

 at N, are parallel to the circular aperture on the lower side 

 of AB. When this is done, the axis LM will be perpendi- 

 cular to the plate AB, and parallel to the axis of vision. 



Having fitted up two or three lenses from the eye of a Par 

 in this manner, I was surprised with the perfection of the 

 magnified image thus obtained, and also with the effect which 

 was produced, when this lens was made the object glass of a 

 compound microscope. A lens of this description will last some 

 hours, and may be preserved for a longer time, either by im- 

 mersing it in the vitreous humor from which it was taken, or 

 keeping it in a moist vessel. This, however, is perhaps un- 

 necessary, as it is so easy to replace it with a new crystalline 

 lens. It is not often that a naturalist requires more than one 

 or two hours observation with a microscope, and if he obtains 

 one which answers his purpose much better than any other, 

 he need not regret the necessity of renewing it. 



Abt. XVIII — Description of a New Self acting- Lever 

 Shiice, and of a Waster Sluice. Invented by Robert 

 Thom, Esq. Rothesay. Communicated by the Author. 



The Lever Sluice, Plate II. Figure 1. 



This apparatus, when placed on a reservoir that supplies 

 any canal, mill, or other work with water, (where the aque- 

 duct between the reservoir and such work is on a level,) will 

 always open of its own accord, and let down the quantity of 

 water wanted by such work and no more ; so that it not 

 only supersedes a waterman, but also saves a great deal of 

 water. 



In Plate II. Fig. 6, AB, is a tunnel through which the wa- 

 ter passes from the reservoir to 



BC, the aqueduct that carries the water to the mills. 



BD, a float that rises and falls with the water in the aque- 

 duct. 



A, an aperture in the mouth of the tunnel. 



