120 PHILOSOPHICAL TRANSACTIONS. [aNNO 16q6. 



tain it. A great many hills are thrown up, called barrows, supposed to be sepul- 

 chral monuments. 



j4 further Account of the IVater Microscope. By Mr. Stephen Gray. N" 223, 



p. 353. 



My water-microscope consists of five parts or pieces of brass, as follow: ab, 

 fig. 3, pi. 3, is the frame of the microscope, which may be about the l6th part 

 of an inch in thickness. At a is a small hole, near the 30th of an inch in diameter, 

 which serves for the aperture of the water, in the centre of a large spherical 

 cavity, about l-8th of an inch diameter, and in depth, somewhat more than 

 half the thickness of the brass ; opposite to this, at the other side, is another 

 concave, only half the breadth of the former, which is so deep, as to reduce 

 the circumference of the small hole, in the centre, to almost a sharp edge ; in 

 these cavities the water is to be placed, being taken upon a pin or large needle 

 and conveyed into them, till there be formed a double convex lens of water 

 which, by the concaves being of different diameters, will be equivalent to a 

 double convex, of unequal convexities. By this means the object is rendered 

 more distinct than by a piano convex of water, or by a double one, formed on 

 the plain surface of the metal ; besides the water is now better secured in its 

 spherical form, cde is the supporter on which to place the object ; if it be 

 water, in the hole g ; if a solid object, on the point f ; this is fixed to the frame 

 of the microscope by the screw e, where it is bent upwards, that its upper part 

 may stand at a distance from the frame ; it is moveable on the screw, as a centre, 

 to the end that either the hole c, or the point f, may be exposed before the 

 microscope, and that the object may be brought to, and fixed in its focus. 

 There is another screw, about half an inch in length, which goes through the 

 round plate into the frame of the microscope a e, the screw and plate taking 

 hold of the supporter about d, where tiiere is a slit, somewhat larger than the 

 diameter of the screw, which is requisite for the admission of the hole c, or 

 point F, according to the nature of the object, into the focus of the glass : for 

 by turning the screw g, the supporter is carried to or from the same, which 

 may be sooner done, if whilst we turn the screw with one hand, the other hold 

 the microscope by the end b, and we continue looking through the water till 

 the object be seen most distinctly. 



The supporter must be made of a thin piece of brass, well hammered, that 

 by its spring it may the better follow the motion of the screw. I chuse rather 

 to fix the supporter by the screw E than by a rivet : because it may now by 

 means of a knife, be unscrewed, and by the other screw g be brought close to 



