VOL. XVI.] PHILOSOPHtCAL TRANSACTIONS. 2|^ 



The immersion was seen at Totteridge (which place is about g miles from 

 London, and nearly 25s. of time to the westward of it) by Mr. Edw. Haines, 

 a member of the Royal Society : who through a gap of the clouds observed the 

 contact of the moon's limb and Jupiter's, at 15h, S^m. the clouds closing 

 again permitted him to observe no more ; however from this we may conclude 

 the central immersion at London to have been 15h.4^m. — The emersion was 

 observed at London by E. Hal ley, at 15h. 49m,; for at 15h. 50m. Jupiter 

 was all out, and the limbs so little separated, that he judged that a minute 

 before, the centre of Jupiter had been on the moon's edge. The point of the 

 emersion was opposite to the southern part of the spot called, by Hevelius, 

 Insula Macra, or at the 342d division of the inner limb of his map of the moon. 



On the Came why Bodies dissolved in Menstrua, specifically lighter than themselves^ 

 swim in them. Ijj> Mr. Wm. Molyneuz,* of Dublin, F.R.S. N° 181, p. 88. 

 Why bodies, dissolved, float in liquors lighter than themselves ; as for in- 

 stance, why mercury, dissolved in strong spirit of nitre, swims in it, though 

 each small particle of mercury be far heavier than so much of the liquor whose 

 place it occupies, is a problem, which Mr. Molyneux thinks cannot be solved 

 by the prime law of hydrostatics, which is, that a body, specifically heavier 

 than a like quantity of liquor, sinks in that liquor ; thus a cubic inch of iron, 

 being heavier than a cubic inch of aqua-fortis, and being put into it, should 

 sink ; and yet we find that iron, being dissolved in a convenient quantity of 

 aqua-fortis, floats in it, and does not fall to the bottom. The reason which 

 my brother gives for this is, that the internal motion of the parts of the liquor 



* Mr. Wm. Molyneux was a good mathematician and philosopher, and a useful member of the 

 Royal Society. Besides a number of papers in the volumes of the Philos. Trans, he was also author of 

 some ingenious books ; as his Sciothericum Telescopium, in l656 ; also a Treatise on Optics, in 1692, 

 in 4to ; and The Case of Ireland Stated, in relation to its being bound by acts of parliament made in 

 England. Mr. M. being born at Dublin 1656, studied at that university ; after which he went to 

 London, and was entered of the Middle Temple. Afterwards returning to Dublin, by his endeavours 

 the Philosophical Society was established there in l683, of which he became the first secretary. 

 The year following he was appointed chief engineer, and surveyor general of his majesty's works. 

 In 16'85 he was elected F. R. S. And in J 689 he left Ireland, and settled with his family at Chester. 

 But in 1692 returned again to his native country, when he was chosen representative in parliament 

 for the city of Dublin, and in l6'95 for the university there. He died in 1698, by a fit of the stone, 

 at only 42 years of age. 



His son, Samuel Molyneux, bom at Chester l689, like the father, was a good scholar, and par- 

 ticularly skilled in optics and astronomy. He applied himself much in improving the telescope; and 

 by means of his apparatus, and with his assistance, it was that Dr. Bradley conducted the astronomical 

 observations on the fixed stars, which led to the celebrated discovery of the aberration of the rays of 

 light. Mr. S. M. bequeathed his scientific papers to Dr. Smith, professor of astronomy at Cambridge, 

 who published them in his noted treatise on optics. 



