Lord Oxmantown on an Apparatus for grinding, {gt, 213 



could not have procured the information they might have de- 

 sired on the subject of Vesuvius, without bringing together a 

 number of unconnected and some scarce works in different 

 languages, and gone through a toilsome and too often unsatis- 

 factory course of reading. Should any thing I may have my- 

 self advanced be considered unimportant or inconclusive, I 

 shall feel satisfied if I have merely simplified the labour of 

 research, or given a stimulus to farther inquiry on an interest- 

 ing, but too much neglected subject. A 



Art. II. — Account of an Apparatus for grinding and polish- 

 ing the Specula of Reflecting Telescopes. By the Right 

 Honourable Lord Oxmantown, M. P. Communicated by 

 the Author. 



In Plate IV. Fig. 2, AB represents the bed of a large power 

 lathe, CD a shaft connected with the steam engine, EF the 

 floor of the room, GH the ceiling, and IK a large lathe head 

 for very heavy work. Motion is communicated by a band from 

 the shaft CD to the lathe IK, and by bands through a succes- 

 sion of wheels, as represented in the figure to the speculum 

 LM. LM, therefore, revolves with amotion slower than VW, 

 in the proportion of the product of the radii of the wheels 

 transmitting the motion to the product of the radii of the 

 wheels receiving it. 



NO represents either the polishing or the grinding tool. PQ 

 is a rod resting against a limber spring RS, and passing through 

 the flat rod TU into a hole in the tool NO. The rod TU is 

 furnished with a joint X, so that when the eccentric VW re- 

 volves, the rod XU reciprocates steadily through the guides 

 Y,Y, carrying with it the rod PQ, and of course the tool NO. 

 From S a weight hangs proportioned to the size of the specu- 

 lum or glass, as the tool alone would be too light. 



To make use of this apparatus the speculum LM is secur- 

 ed to the centre of the chuck, as represented in the figure, by 

 means of very soft pitch and wooden pegs driven into the 

 chuck. The tool NO of lead and tin of the proper curve is 

 then placed upon it, and the rods PQ and TU arranged as in 

 the plate. At the commencement of the operation, to expedite 



