VOL. XLVIII.] PHItOSOl'HICAL TRANSACTIONS. SSQ 



in the skin ; both which causes may be removed by the strong acid in this water. 

 It is an excellent detergent for scorbutic ulcers, as Hoffman justly observes. It 

 has already performed several remarkable cures of this kind. Dr. B. had often 

 recommended it in such cases with success, joined with proper internal medi- 

 cines. How far the success of practice in the miners, who drink it frequently, 

 might be depended on, longer experience must determine. Certainly, a great 

 allowance must be made for the strength of their constitutions, and the insensi- 

 bility of their nerves, constantly exposed to the noxious steams of damp pits. 

 He never ventared to prescribe it internally : and as the materia medica affords 

 vomits and purges of a more innocent kind, he thought it in that respect unne- 

 cessary. He had reason to imagine, from the effects which this water had on 

 some earth-worms, that it was a very powerful anthelminthic, if cautiously 

 given. 



Some fresh filings of iron, put in this water, soon precipitated all the copper, 

 and made it a strong and agreeable chalybeate. Hence it might be used as a sub- 

 stitute for spa-water, the virtue of which depends on the iron. Some prepared 

 filings of iron remained 8 days in this water ; without producing the least alter- 

 ation. Hence it appeared, that this medicine could have but a weak effect, if 

 any at all, in absorbing acids in the first passages. 



XXIX. On Mr. Gascoigne's Invention of the Micrometer. By Doctor 



Bevi.1, p. igo. 



Though Mr. Townley, in his paper printed in the Philos. Trans. N" 25, p. 

 457, has sufficiently made it appear that the invention of the micrometer w<ls 

 Mr. Gascoigne's, and that he applied it to measuring small angles in the heavens, 

 and for settling the moon's parallax, long before Messieurs Auzout and Picard 

 thought of any such matters ; yet are the French astronomers apt to ascribe it to 

 their countrymen, without so much as once mentioning the name of Mr. Gas- 

 coigne. No sooner had the late Dr. Derham restored the application of teles- 

 copic sights to quadrants to its true author Mr. Gascoigne, than M. de la Hire, 

 who never made the doctor any reply on that head, took occasion, in the me- 

 moirs of the Royal Academy of Sciences for 1717, to ascribe this contrivance of 

 the micrometer to M. Auzout, in conjunction with M.' Picaixi ; alleging, for 

 proof, an extract of a letter, dated Dec. 28, 1 666, from M. Auzout to M. Ol- 

 denburg, and printed in the Phil. Trans. N° 21. Several others have since co- 

 pied M. de la Hire's assertion, and last of all, M. Bouguer, in the memoirs of 

 the Royal Academy of Sciences for 1748, lately publishetl, where he describes 

 an instrument which he calls a heliometer ; the contrivance of which seems in 

 every respect the same as that sent about 10 years ago to the Royal Society, by 

 Servington Savery, Esq. 



VOL. X. . 3 3 



