102 



ON DIVIDING ASTRONOMICAL INSTRUMENTS. 



Invented by 

 Mr. Hindley 



Lantern '< 

 employed. 



jointed together so as to give to the cutter an easy motion 

 for drawing lines directly radiating from the centre,^bnt in- 

 flexible with respect to lateral prcssare ; del are its handles. 

 The cutting point is hidden below the microscope H; il is 

 of a conical form, and were it used as a dotting point, it 

 would make a puncture of an elliptical shai>e, the longer 

 diameter of which would point towards the centie. This 

 beautiful contrivance, now well known, we owe to. the inge- 

 nuity of the late Mr. Hindley of York ; it was borrowed by 

 Mr. Ramsden*, and applied with the best effect to his di- 

 viding engine. 



It might have been mentioned sooner, that in the instance 

 which I have selected as an example of my dividing, the 

 operation took place when the season of the year, and the 

 smoke of London, had reduced the day to scarcely six hours 

 of effective l)ght; and rather than confine my labours within 

 such narrow limits, I determined to shut out the day-light al- 

 together. Fig. 7 shows the construction of the lanterns which 

 I used. A very small wick gave sufficient light, when kept 

 from diverging by a convex lens ; while the inclining nossel 

 was directed down exactly upon the part looked at, and the 

 light, having also passed through a thin slice of ivory, was 

 divested of all glare. I enter into this description, because, 

 I "think, I never saw my work better, nor entirely to so 

 much advantage as in this instance ; owing, perhaps, to the 

 surrounding darkness allowing the pupil of the eye to keep 

 itself more expanded, than when indirect rays are suffered 

 to enter it. The heat from a pai' of these lanterns was very 

 inconsiderable, and chiefly conducted along with the smoke 

 up the reclining chimney. 



Previous to cutting the divisions, the parts now described 

 for cutting ihe must be aditi:^ted. The cutting apparatus must be placed 

 divisions. •,,,•• t • , i , , , ^ 



with the dividmg point exactly at the place where the first 



line is intended to be drawn, and clamped, so that the ad- 

 justing screw may be able to run it through a whole inter- 

 val. The microscope H must be firmly fixed by its two 

 pillars bb to the main frame, with its micrometer head at 

 zero; and with its only wire In the line of the radius, bi- 



* This I learned from that most accurate artist Mr. John Stancliffe, 

 wlio was himself apprentice to Hindley, 



secting 



Prepavation 



