381 



Aur. XV. ASTRONOMICAL AND NAUTICAL COL- 

 LECTIONS. No. VIII. 



i. Report on the present State of Ramsdcn's Dividhig Eiic/ine, 

 By Dr. W. H. Woi,l.\ston. Published by Permission of the 

 Board of Loxgitlde. 



Since the Dividing Engine belonging to the Board of Longi- 

 tude appeared lo Captain Kater and myself, from our examina- 

 tion of the divisions made by it, to be more defective than any 

 other engine examined by the same means, we thought it de- 

 sirable that this engine should be used a second time, with all 

 possible care, to rc-divide the double circle constructed for the 

 purpose of this inquiry. 



Mr. Cary readily undertoolc to repeat the operation, with 

 attention to all the precautions that appeared necessary. 



In the measurement of this second set of divisions, which 1 

 commenced shortly afterwards, I discovered that the divisioiiS 

 upon the outer circle, though made at the same time with those 

 on the inner circle, and by the same motion of the cutting-point, 

 were not coincident with them, as had been presumed to be the 

 case in our former examination ; and that it consequently became 

 necessary to alter the mode of examination, which had been 

 pursued under that presumption. 



It is in fact the inner circle alone that really needs to be 

 measured. For, since the motion of the cutting-point in marking 

 the divisions is from the centre outwards, the inner circle must 

 be regarded as a more correct copy of the engine than the outer, 

 of which the divisions are liable to be misplaced by any irregu- 

 larity, given to the motion of the cutter, in its passage over the 

 line of contact Ijctween the inner and outer circle. In any 

 examination by aliquot parts, (as by fiths,) when any one arc on 

 the outer circle has been compared with each arc of the inner 

 ill succession, and tlie diflferenccs measured, the sum of lluse 



