434 PHILOSOPHICAL TRANSACTIONS. [aNNO 1 699. 



water seem to observe the simple proportion of their gravities directly, as I have 

 compared them in the following table. The numbers there expressing the re- 

 fraction of water are taken from the mean of nine observations at so many several 

 angles of incidence made Jan. 25, l64^, by Mr. Gascoigne (the ingenious first 

 inventor of the micrometer, and the ways of measuring angles by telescopes), 

 and those of air are produced by the experiment above related, &c. 



Water. Air. 



The assumed sines of the angles of incidence through 100000 100000 



The sines of the correspondent angles of emersion out of 134400 100036 



The refractive power of. 34400 36 



Spec. grav. (if as 900 to 1 at the time of the experiment) of) f 38 



or (if as 850 to I ) of } (.40 



From hence it seems very probable, that their respective densities and refrac- 

 tive powers are in a just simple proportion, and if this should be confirmed by 

 succeeding experiments, made at different angles of incidence, and with cylin- 

 ders continuing exhausted through several changes of the air, it would be more 

 than probable that the refractive powers of the atmosphere are every where, and 

 at all heights above the earth, proportional to its densities and expansions. And 

 hence it would be no difficult matter to trace the light through it, so as to ter- 

 minate the shadow of the earth ; and, together with proper expedients for mea- 

 suring the quantity of light illuminating an opaque body, to examine at what 

 distances the moon must be from the earth to suffer eclipses of the observed 

 duration. 



The Julian Account not to he changed for the Gregorian. By Dr. JFallis. 



N°257, p. 343, 



That in our ecclesiastical computation of the Paschal tables there is some 

 disorder, is not to be denied ; yet an alteration may be attended with still greater 

 inconvenience. A thing of moment when once established should not be rashly 

 altered. In the business of geography, by removing the first meridian on some 

 plausible pretence from where Ptolemy had placed it, though a thing at first 

 purely arbitrary, it is now come to pass that we have, in a manner, no first 

 meridian at all ; every new map-maker placing his first meridian where he pleases, 

 which has created much confusion. 



And, as to the disorder in the Paschal tables, it was a thing observed and 

 complained of for 3 or 400 years, before Pope Gregory unhappily attempted the 

 correction of the calendar. But it was all that time thought advisable rather to 

 suffer that inconvenience than, by correcting it, to run the ha/.ard of a greater 

 mischief. And it had been much better if it had so continued to this day. 



