VOL. XLVI.] PHILOSOPHICAL TKANSACTIONS. 67 



glass cap performed much the same with the others. He had 1 of them polished 

 again by Mr. Smeaton; and in company with him repeated the same experi- 

 ments ; but with no better success. The agate cap made always many more vi- 

 brations than the glass one ; and generally with the latter the number diminished 

 by repeated trials ; whereas with the agate cap it usually increased. 



These experiments made him lay aside the glass caps, and put him on think- 

 ing how agate ones might be made with as little expence as possible. With this 

 view he got a cap turned of ivoiy, in such a manner as to receive a small bit of 

 agate at the top. This being ground concave, and polished on that side, where 

 it formed the apex of the hollow cone in the cap, was capable of answering the 

 purpose as well as if the whole had been agate, and was much lighter. These 

 caps may be made cheap enough for common use ; and if good at first cannot 

 easily be impaired. 



For a point, he chose a common sewing needle, and contrived to fix it in such 

 a manner as to be taken out with the greatest ease, and replaced by another, if 

 necessary ; by which means an excellent point may be always had with little 

 trouble or expence. Common needles, when well tempered, have all the quali- 

 fications that can be desired for the purpose intended. The smallest are strong 

 enough to bear the weight of a card ; and are neither so soft as to be liable to 

 bend, nor so hard and brittle as to break ; and the}' are generally better pointed 

 than any that a common workman could pretend to make extempore. 



The specimen of the improved compass, shown to the Society, was made by 

 Mr. Smeaton, a gentleman whose uncommon skill in the theory and practice of 

 mechanics has enabled him to execute whatever Mr. K. proposed in such a man- 

 ner as always to exceed his expectations : and not only so, but Mr. S. added a 

 considerable improvement of his own. By a very simple contrivance he made 

 the same instrument capable of serving the purposes of an azimuth and amplitude 

 compass ; and that in a manner much preferable to any thing hitherto contrived; 

 the description and use of which he has drawn up himself, for the perusal of the 

 Society, as follows. 



On some Improvements of the Mariner s Compass, in order to render the Card 

 and Needle proposed by Dr. Knight, of General Use. By John Smeaton, * 

 Philosophical Imtrument-maher. N" 495, p. 513. 



The cover of the wooden box being taken off, the compass is in a condition to 

 be used in the bittacle, when the weather is moderate : but when the sea runs 



•John Smeaton, a celebrated engineer, was born 1724, at Austhorpe, near Leeds j wherp. 

 also he died in 1792, in the 69th year of his age. Mr. S. seems to have been born an engineer. The 

 originality of his genius, and the strength of his understanding, appeared at a very early age. His 



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