114 
POPULAR SCIENCE REYIEW. 
PHYSICS. 
A New Ozonometric Method. — At tlie meeting of tlie Prencli Academy, on 
tlie 9th of December, MM. Berigny and Salleron presented a paper describ- 
ing a new process they have adopted for the registration of the proportion of 
ozone present in the atmosphere. Instead of exposing the test-paper for 
twelve hours to the action of the air, and of comparing it then with a 
standard chromatic scale,” they place the paper in an instrument they 
have constructed which they tenn the Chronozonomete)'. This consists of a 
drum moved by clockwork, which unfolds the paper to the air with a 
definite velocity, and thus exposes it to atmospheric action in uniformly 
increasing periods. Suppose, for example, that this apparatus unfolds the 
test-paper with the velocity of a centimetre per hour ; after twelve hours 
there will be a length of paper exposed equivalent to twelve centimetres. 
The first centimetre of the paper will have been exposed for twelve hours, 
the second for eleven hours, and so on to the last, which will only have 
been exposed one hour. If this strip of paper is plunged into water it will 
become tinged with a graduated scale of colour from white to dark violet. 
Here, then, the test-paper supplies its own standard of comparison j for, to 
take a rough example, if the twelfth centimetre be as deeply tinted as the 
first one, it will be evident that the proportion of ozone present in the air 
during the twelfth hour was as great as that present during the remaining 
eleven, — ^Vide NlnstiM, Dec. 11. 
Actinic Power of Ahsorhed Light . — M. Niepce de Saint- Victor, the cele- 
brated French physicist, has recorded a discovery which is most unexpected, 
but which is only another illustration of the principle by which force is 
never lost. As the result of some late researches, he announces the extra- 
ordinary fact that porous or rugose surfaces which have been exposed to 
light have a definite decomposing action on salts of silver when placed in 
contact witli them in the dark. It has been considered probable by many- 
natural philosophers that phenomena like phosphorescence are due to the 
emission of light previously absorbed. Till M. Saint- Victor’s discovery 
this hypothesis had little beyond vague speculation to support it, but now 
it becomes an established theory. The French savant has proved by various 
photographic experiments that pieces of pasteboard which have been ex- 
posed to the light give out actinic force in the dark, and may be employed 
in producing decomposition of silver-salts. 
The Bessemer Steel Spectru7n . — Father Secchi, who lately presented to the 
French Academy his fine memoir on the Stellar Spectra, compared the 
spectra of certain yellow stars with the spectrum produced in the Bessemer 
converter ” at a certain stage of the process of manufacture. The employ- 
ment of the spectroscope in the preparation of this steel was begun a couple 
of years since, but the comparison of the Bessemer spectrum with the spec- 
trum of the fixed stars has not, so far as we can remember, been made before. 
The Bessemer spectrum is best seen when the iron is completely decarbonized j 
it contains a great number of very fine lines and approaches closely to the 
spectrum of a Orionis and a Herculis. The resemblance, no doubt, is due to 
the fact that the Bessemer flame proceeds from a great number of burning 
metals. The greatest importance attaches to the analogy pointed out by 
