446 fHILOSOPHICAL TRANSACTIONS. [aNNO 1740. 



secured his objects in sliders, as we at present do, and have contrived some 

 such means as ours, of screwing his several glasses of different magnifying 

 powers, occasionally, to one and the same instrument, and of applying his 

 sliders to which of them he judged best. A few good glasses, gradually mag- 

 nifying one more than another, would, by such a method, have answered all 

 the purposes of his great number, and his objects would have been preserved in 

 a much better manner. 



Passing over the different microscopes invented by Wilson, Marshal, Cul- 

 pepper, Scarlet, and others, though all deserving praise, Mr. B. notices two 

 extraordinary improvements lately made ; viz. the solar or camera obscura 

 microscope, and the microscope for opaque objects. But these inventions are 

 by the ingenious Dr. Liberklmn. Mr. Cuff, in Fleet-street, has taken great 

 pains to improve and bring these to perfection ; and therefore the apparatus 

 prepared by him is wiiat are described below. 



This solar microscope is composed of a tube, a looking-glass, a convex lens, 

 and a n)icroscope. The tube is of brass, near 2 inches in diameter, fixed in a 

 circular collar of mahogany, which, turning round at pleasure, in a square 

 frame, may be adjusted easily to a hole in the shutter of a window, in such a 

 manner, that no light can pass into the room but through the tube. Fastened 

 to the frame by hinges, on the side that goes without the window, is a looking- 

 glass, which, by means of a jointed brass wire coming through the frame, may 

 be moved either vertically or horizontally, to throw the sun's rays through the 

 brass tube into the darkened room. The end of the brass tube without the 

 shutter has a convex lens, to collect the rays, and bring them to a focus ; and 

 on the end within the room, Wilson's pocket microscope is screwed, with the 

 object to be examined applied to it in a slider. The sun's rays being directed by 

 the looking-glass through the tube upon the object, the image or picture of the 

 object is thrown distinctly and beautifully on a screen of white paper, and may 

 be magnified beyond the imagination of those who have not seen it. Mr. B. 

 assisted lately in making some experiments by means of this instrument, and a 

 particular apparatus contrived by Dr. Alex, Stuart, for viewing the circulation of 

 the blood in frogs, mice, &c. and had the pleasure of beholding the veins and 

 arteries in the mesentery of a frog magnified to near 2 inches diameter, with 

 the globules of the blood rolling through them as large almost as peppercorns. 

 They examined also the structure of the muscles of the abdomen, which were 

 prodigiously magnified, and exhibited a most delightful picture. 



The microscope for opaque objects remedies the inconvenience of having the 

 dark side of an object next the eye ; for by means of a concave speculum of 

 silver, highly polished, in whose centre a magnifying lens is placed, the object 



