( 138 ) 
[January, 
PROGRESS IN SCIENCE. 
PHYSICS. 
Light. — Some useful experiments showing the a&ion of Light on Ebonite 
have been described in “ Nature,” by Prof. McLeod, of the Royal Indian 
Engineering College, Cooper’s Hill. It is, he says, well known to electricians 
that the insulating power of ebonite gradually diminishes, in consequence of 
the formation of a conducting layer of sulphuric acid on the surface; but it is 
not so well known that exposure to light facilitates this change, if indeed it is 
not an essential condition. He noticed that an ebonite plate eleCtric machine 
which had been kept in a light room had changed in colour, except on those 
portions which had been protected from light by the rubbers. The exposed 
surface acquired a brown colour, and the machine aCted very badly. On 
cleaning the plate with a hot solution of caustic soda, large quantities of 
ammonia were evolved, and the brown surface became softened, so that it 
could be easily scraped off. He therefore cut a plate of ebonite into four 
pieces, each about 52 m.m. long, 22 m.m. wide, and 8 - 5 m.m. thick, and one- 
half of each piece was varnished with an alcoholic solution of shellac. Two 
pieces were placed in test-tubes plugged with cotton-wool, the other two being 
sealed hermetically in similar tubes. One of each of these tubes were placed 
in a dark drawer, and the other pair exposed to light in the laboratory, and 
during the latter part of the experiment to direct sunlight. About nine months 
afterwards the tubes were opened, the ebonite washed with water, and the 
amount of acid determined by standard solution of caustic soda. No trace of 
acid could be dete&ed on either of the pieces of ebonite which had been kept 
in the dark ; on the one which had been exposed to light in the closed tube 
o'343 m.grm. of sulphuric acid was found ; and on the other, which for three 
weeks had been exposed to both light and air, 2'646 m.grms. 
We learn, from the same journal, that Dr. Janssen is devising the construc- 
tion of an automatic photographic revolver which will take a photograph of 
the sun every hour, each day of the year, from sunrise to sunset. The photo- 
graphs which will be taken under cloudy conditions will be useless so far as 
sun-spots are concerned, but they might be utilised for meteorological pur- 
poses. The others will be kept and tabulated. The advantage of this 
plan is that it will dispense with any observer, and will obtain a mechanical 
regularity. 
We have received from Mr. Todd, the Postmaster-General and Superinten- 
dent of Telegraphs and Government Astronomer of South Australia, a 
pamphlet entitled “ South Australia, its Observatory and Meteorology.” The 
Observatory is situated on the West Park lands, having the city of Adelaide 
andthe Mount Lofty Ranges on the east, and St. Vincent’s Gulf — towards which 
the land gently slopes — at a distance of about 5 miles on the west. Until 
recently its operations were chiefly confined to Meteorology, but advantage 
was taken of the transit of Venus in 1874 to procure a 10-feet equatorial by 
Cooke and Son, of York, and other instruments will shortly be added. Mr. 
Todd is anxious to turn the Observatory to account in the promotion of high- 
class education, by the delivery at the Observatory of le&ures to students on 
Physical Science. In a recent Report to the Government he says that the 
Observatory is required not so much for the furtherance of astronomical 
science as for educational purposes. It will be able to render valuable aid in 
those fields of astronomical research which do not involve continuous observa- 
tion or heavy computations — such work, for instance, as solar and stellar 
spedtroscopy, sun-spots, double stars, and what Sir G. B. Airy has pointed out 
as a great want, observations of occultations, eclipses, and transits of Jupiter’s 
