VOL. IX.] PHILOSOPHICAL TRANSACTIONS. 177 



Newton's new theory of light and colours, grounded upon an experiment of 

 letting the sun-beams through a little hole into a dark chamber, seems to need 

 no other answer but this, that you would be pleased to look upon and consider 

 the scheme in Mr. Newton's 2d answer to P. Pardies in Numb. 85 of the Phil. 

 Trans, and rest assured, that the experiment, as it is represented, was tried in 

 clear days, and the prism placed close to the hole in the window, so that the 

 light had no room to diverge, and the coloured image made not parallel, as in 

 that conjecture, but transverse to the axis of the prism. 



Extracts of Two Letters, ivrittten by Mr. Flamsteed to Mr. Collins ; tJie one of 

 Nov. 25, 1674, concerning an Instrument to show the moons true place to a 

 minute or two ; as also the PVriters design of correcting the hitherto assigned 

 Motions of the Sun, The other of Dec. 14, 1674, on the necessity of making 

 New Solar Numbers, together with an Expedient for making trial, whether the 

 Refractions in Signor CassinCs Tables are Just. London, Dec, 17, 1674. 

 N°110, p. 219. 



The Extract of the first Letter. 



After my return to Derby, I perused Mr. Street's discourse, and considered 

 the contrivance of his moon-wiser ; which, though he affirms in the conclusion 

 of his little tract, to be different from Mr. Horrox's ; yet I can assure him, that 

 for the motion of longitude it is the^-ery same, and no other than what is taken 

 from my explication ; save that, where I thought the manner of librating the 

 apogaeum was obvious from the calculation, and needed not to be explained, he 

 has shown how to take it in the libratory circle. As for his motion of latitude, 

 indeed that is a little different ; but I can again assure him, not much better 

 than Mr. Horrox's, to whom we are indebted for this contrivance. Mean- 

 time, when he has done what he can, it will not show the true place to half a 

 degree. 



I have therefore thought of another contrivance, not so large nor trouble- 

 some as his, that shall show the moon's true place to a minute or two, 

 without error, and with an instrument no larger than his, to less than a single 

 minute. 



And because I find, by correcting the sun's motions by Signor Cassini's obser- 

 vations, that his inequalities are 5 minutes less in his mean distance ; and that 

 the motion of latitude needs correction ; I shall amend both, as I think and find 

 fit, in this instrument ; which with the place and latitudes will give the moon's 

 semi-diameters and parallaxes to a second. 



TOL. II. A A 



