1Q4 PHILOSOPHICAL THANSACTIOKS. [aNNO IjdS. 



between the white and the black or copper-coloured, according as the parents 

 are, even to decompounds, as a Mulatto-fina, the child of a Mulatto man and 

 Mostesa woman, &c. But neither is the child of a man and woman of these 

 white Indians white like the parents, but copper-coloured as their parents were. 

 For so Lacenta told me, and gave me this as his conjecture how these came to 

 be white, that it was through the force of the mother's imagination looking on 

 the moon at the time of conception; but this I leave others to judge of. He 

 told me also that they were but short-lived." 



N. B. Lacenta was the king of the Indians among whom Mr. Wafer lived. 



F7/. Of an Improvement made by Mr. Peter Dollond in his New Telescopes : in 

 a Letter to James Short, M. A., F. R. S., with a Letter of Mr. Short's to t/ie 

 Rev. T. Birch, D.D., Secret. R. S. Dated Surry-street, Feb. 7, 1765. p. 54. 

 " Inclosed is a letter (says Mr. S.) which I received this morning from Mr. 

 Dollond, concerning an improvement which he has made in his new telescopes. 

 He, some months ago, sent me a telescope, in this new way, of 34- feet focal 

 length, with an aperture of 3^ inches; I examined it, and I approved of it; I 

 have tried it with a magnifying power of 150 times, and I found the image dis- 

 tinct, bright, and free from colours." 



I take the liberty, says Mr. Dollond, of sending you the following short ac- 

 count of an improvement I have lately made in the compound object glasses of 

 refracting telescopes. The dissipation of the rays of light may be perfectly cor- 

 rected in object glasses, by combining mediums of different refractive qualities; 

 and the errors or aberrations of the spherical surfaces may be corrected by the 

 contrary refractions of two lenses, made of the different mediums; yet as the 

 excess of refraction is in the convex lens, and though the surfaces of the concave 

 lens may be so proportioned as to aberrate exactly equal to the convex lens, near 

 the axis; yet as the refractions of the two lenses are not equal, the equality of 

 the aberrations cannot be continued to any great distance from the axis. 



In the year 1758, when my father had constructed some object glasses for 

 telescopes in this manner, viz. with one convex lens of crown glass, and one con 

 cave lens of white flint glass ; he attempted to make short object glasses to be 

 used with concave eye-glasses, in the same manner; but as the field of view, in 

 using a concave eye-glass depends on the aperture of the object glass, the limits 

 of the aperture were found to be too small; this led my father to consider, that 

 if the refraction of the crown glass, in which the excess was, should be divided, 

 by means of having two lenses made of crown glass instead of one, the aberra- 

 tion would thereby be decreased, and the apertures might then be larger: this 

 was tried with success in those object glasses, when concave eye-glasses were 

 used, and these have been ever since made in this manner: some trials were like- 



