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Abstract of a Memoir read before the Wernerian Society^ gi- 

 ving an account of Experiments directed to ascertain the 

 Principles ofAttractwn and Repidsion in the Lunar Rays, 

 Sfc. ; a Description of several Varieties of the Instruments 

 cmistructedjor that purpose ; and some Applications of the 

 Observations made, as illustrative of other Subjects. By 

 Mark Watt, Esq. Member of the Wernerian Society, &c. 



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JL HIS paper commenced by some remarks on the unsuccessful 



attempts that had been made, to determine whether the Junar 

 beam had any calorific properties or not. And, laying this sub- 

 ject altogether aside, the author considered it more probable, 

 that he might succeed in exhibiting, with sufficient certainty, 

 the attractive influence of the moon ; a principle which it was 

 generally acknowledged to possess, from the coincidence of its 

 monthly revolutions with the flux and reflux of the sea. The 

 received calculation also being, that the attractive power of the 

 moon upon our globe, when contrasted with that of the sun, was 

 as 10 to 3, from her greater approximation to the earth. 



The different forms of the instrument used for making ob- 

 servations on the attracting and repelling powers of different de- 

 grees of light, were constructed on the same plan, with a view to 

 the greatest specific lightness, and the least possible friction, 

 that moti<m might be produced by the most delicate impulses 

 of hght. 



About 6 inches of the opaque part of the quill of any feather 

 pf a suitable size, was used as a balancing bar, which was made 

 ,,^o revolve on a fine steel point, by means of a small agate cap- 

 sule inserted into an aperture made in the quill, at about Jd of 

 the length of the bar from the point to which the discs were at- 

 tached. No fixture was used for the cap, the elasticity of the 

 "liiedullary part oiP the quill holding it with sufl^cient firmness. 

 The discs being affixed to one extremity of the quill, were ba- 

 lanced by any small weight at the other, and they traversed like 

 a compass-needle. 



The following substances were tried : A circular piece of 

 dark coloured velvet, about 4 or 5 inches diameter, stretched on 



