498 PHILOSOPHICAL TRANSACTIONS. [aNNO 1681. 



Hipparchus's period of 304 years, had 1 11035 days, its 8th part is. . 13879f 



Whereas my 38 years period has but just days 13879 



I have chosen rather to take the revolution of the moon than that of the sun, 

 for my chief and primary measure of time; because, first, the hmar phases, 

 and consequently months, are more easily discerned than the sun's annual 

 period, even by the meanest capacity : next, the observations on the moon have 

 been more numerous, more exact, and of far greater antiquity; astronomers 

 having also had the help of eclipses of very distant ages for their guide, in find- 

 ing out very nearly the true measure of the moon's mean motion : lastly, keep- 

 ing an account by the moon, we may reckon by the sun also, that is by months 

 and years too; whereas, on the contrary, reckoning by a solar year, months are 

 only empty names, and in measuring of times and seasons the moon is rendered 

 of no use. 



A New Lamp. By Robert Boyle, Esq. Philos. Collect. N° 2, p. 33. 



. In fig. 5, pi. 14, ABCD is a vessel of latten, well soldered. BC, EF, are 

 two bottoms soldered to the vessel. FG is a pipe soldered to the bottoms afore- 

 said, the aperture being in the great cavity FA. H is a hole in the pipe FG, 

 opening between the two bottoms B C, EF. I is another hole to which is soldered 

 a pipe I G bent upwards at G. PP is a small vessel fit to receive the wick of the 

 lamp. LM is a slender pipe open at both ends, and soldered to the cover AD 

 at L, and to the bottom EF at M; so that by that pipe the external air may 

 communicate between the two bottoms, without penetrating into the cavity AF. 

 N is a short pipe soldered to a hole in the cover AD, so that thereby oil may be 

 poured into the cavity AF; and stopped afterwards close with cork. 



For filling up this machine, stop the aperture G of the pipe IG with a long pin 

 fitted for that purpose, as also the upper end of the pipe LM; then pour in the 

 oil by the aperture N; which done, the aperture N is to be shut up exactly, and 

 both the others, G and L to be opened. Then the oil will run through the 

 pipe IG, and fill the vessel P, till its surface be on the same level with the 

 hole H. 



Now it is easy to see that this lamp is free from all the inconveniencies that 

 Cardan's lamp is subject to. For, first, the air does not get into it by starts as 

 it does in Cardan's lamp ; but when the oil in PP is wasted, and comes to have 

 its surface lower than the hole H, the oil from the cavity AF runs gently into 

 PP, because its place in the cavity AF is easily supplied by the external air, 

 which gets up into the said cavity AF, through the pipe LM and the hole H. 

 Secondly, when the air contained in the cavity AF comes to be rarefied by heat, 

 it drives out much oil, and so may choak up Cardan's lamp; but in this the oil. 



