92 ANNUAL OF SCIENTIFIC DISCOVERY. 



plate -from slipping away. This frame carries in its centre a round rod, 

 standing vertically, which is kept in its place by two bars fastened to the 

 frame of the machine. This arrangement prevents the frame from moving 

 away, but does not prevent it from revolving. There is room on a circular 

 table for four glass plates, disposed in a similar manner, at a distance from 

 the centre. A trough full of sand, with an aperture in the bottom propor- 

 tional to the quantity of sand required, is suspended above. The machine 

 is put in operation by making the ten feet table revolve. The frames above 

 being held in their place, the glass they carry is rubbed by the table, and 

 the velocity being greater at the circumference of the table than near the 

 centre, these frames themselves begin to revolve in a contrary direction. 

 This motion, which is a result of the first, has the advantage of regulating 

 the friction by successively bringing every point of the glass near the centre, 

 where the friction is least, and near the circumference where it is greatest. 



The polishing machine is nearly similar to the grinding machines. The 

 only difference is that its upper surface is formed of wooden rings covered 

 with felt, which are screwed upon the cast-iron table, and that these circular 

 rings are eccentric to the table, and leave between them parallel circular 

 ridges of nearly the same breadth as the wooden rings. The glass plates 

 are placed upon this machine as upon the other, in exactly the same manner, 

 but instead of sand falling on it from a box, oxide of iron or rouge, 

 thoroughly mixed with water, is used, and is applied to the felt with a 

 brush. 



The polishing and grinding of plate glass has, heretofore, been effected by 

 manual labor. By the above described apparatus, a result formerly requir- 

 ing ten hours of labor, is said to be accomplished in one. 



JOPLIXG'S JMPEOVED WATER METEE. 



At a recent meeting of the Institution of Civil Engineers, Mr. T. T. Jop- 

 ling described a metre of his own invention constructed on the piston princi- 

 ple, which appeared to meet the objections hitherto made to that class of 

 metre. It consisted of two measuring cylinders, set parallel to each other, 

 with working pistons, the rods of which projected out of the cylinders in 

 opposite directions, canying at then' extremities slide valve frames, for sup- 

 porting and operating on the slide valves that governed the ports of the 

 cylinders. These measuring cylinders were contained in a cast-iron case or 

 tank, into which the water to be measured entered under a certain pressure. 

 The water thence passed into the cylinders, from which, after having acted 

 upon one or other of the pistons, it made its escape. Through the agency 

 of suitable counting apparatus connected with one of the piston rods, the 

 reciprocating movements of the piston were counted, and thus the quantity 

 of water passed through the metre, in a given time, was indicated. The 

 measuring chambers were made somewhat like ordinary steam engine cylin- 

 ders, as respected the inlet and outlet ports ; but in one of the cylinders the 

 direction of the inlet ports was inverted, in order that the right hand port might 

 pass the water to the left hand end of the cylinder, and the left hand port to 

 the right hand end. By this means the two pistons were enabled to follow 



