18 On the apparent Changes 



Riccioli and Grimaldo state, the observed diameter of the 

 sun in the horizon to be from 45 to 60 minutes, of the moon 

 from 38 to 40 minutes. 



Molyneux objects that the moon ought to have appeared 

 under an angle of 5 degrees. Did any person ever see the 

 moon extended under an angle of 5 degrees in the horizon ten 

 times larger than usual ? This argument then fails in fact, as 

 does also the other, that there is no refraction or change of 

 place but the vertical, and therefore no dilatation. 



I agree with Riccioli and Grimaldo ; because their measure- 

 ments accord v^ith the theory hereafter to be developed ; because 

 they agree in their amount with the appearances, vertical as 

 well as horizontal; and because of their very differences ; for of 

 the sun and moon, the mean apparent diameters are nearly 

 equal, and severally about 32' and 31', and according to their 

 observations, the measure ji diameters are from 45' to 60' of 

 the sun in the horizon, from 38' to 40' of the moon, the weaker 

 marginal light of the moon being extinguished, and her size 

 more reduced by the atmosphere through which she appears, 

 than that of the sun. 



The size of a candle, viewed through different deeply-coloured 

 glasses, is considerably diminished by the loss of its fainter 

 marginal light ; and so the sun and moon ought, on account of 

 the loss of light in passing through the atmosphere, to appear, 

 and would appear, diminished in diameter, but that this cause 

 of diminution is more than compensated for, and the discs are 

 more enlarged by, the lateral inflection of the rays than di- 

 minished by the extinction of the marginal light. By the in- 

 creased extinction, however, of the weaker marginal light of the 

 moon, her apparent size is more reduced than that of the 

 brighter and more strongly illuminated sun, the atmosphere, 

 through which they both are seen, acting as a coloured glass, 

 giving colours to both luminaries in different degrees and pro- 

 ducing these differences in the measurements of Riccioli and 

 Grimaldo. 



Thus the theory to be hereafter developed, confirms the ob- 

 servations of Riccioli and Grimaldo made, particularly upon 



