32 



to obtain more than half the result I had hoped for. A few 

 thin clouds, moreover, interfered materially with the 

 observations. 



The satellites were disposed two on each side the planet. I 

 missed all the contacts of the satellites, except those of the 

 third (in order), which I got, both at immersion and emersion. 

 I also missed the first contact of the planet. 



I timed the observations by the sidereal clock, afterwards 

 reducing to local mean time. I may here explain that my 

 clock is with my smaller telescope in the adjoining grounds 

 (Mr. Pullen's garden). I get the time from it to the large 

 telescope by an electric line communicating motion each 

 minute to the hands of a dial, and the clock beats (seconds) I 

 get by telephone. This is just where the trouble came in ; 

 the clatter of the wind interfering with my keeping correct 

 count. The times recorded, however, I obtained with certainty, 

 and fair accuracy, as follows : — 



hrs. min. sec. 



1st Contact of planet (missed) 



2nd Contact (or total disappearance)... 



3rd Satellite disappeared at 



At re-appearance — 



The planet just peeped out at 



And emerged entirely at 



Third satellite re-appeared 



As seen in the 8|-in. reflector (power 200, full aperture), 

 the phenomenon furnished a most interesting exhibition. To 

 ■watch the beautiful markings of the planet gradually disappear- 

 ing behind the dark limb of the moon, and the extinction of 

 the satellites one by one, and still more, the re-appearance in 

 the same order, was almost enough to distract the attention 

 from the sterner details of minutes and seconds. 



Whilst in close proximity, and especially at re-appearance, I 

 carefully studied the relative luminosity of the moon and 

 planet, especially with reference to the question of the planet's 

 being in any degree self-luminous. I here became aware of 

 my mistake in having omitted to provide some means of 

 photometry. However, as an eye estimate, I was struck with 

 the apparent smallness of the difference in the luminosity of the 

 two bodies, as compared with their vast difference of distance from 

 the sun. Considering that the sun's disc, from the distance of 

 Jupiter, compared with the same as viewed from the moon 

 (or earth), would appear only as about 1 to 25 in surface, I 

 could not but feel impressed with the fact, that the brightness 

 of the planet was out of all proportion to the relative amount 

 of light received by him from the sun. As compared with the 

 lunar surface, it appeared as if the shadow of a thin cloud 

 were cast upon the planet. Still, as against the theory of the 

 planet's being self-luminous by his own glowing heat (as has 



9 



25 



27-8 



9 



33 



37'6 



10 



2 



49'8 



10 



6 



23'2 



10 



14 



14 



