1866. | De la Rue and Celestial Photography. 363 
six feet in diameter, which is being laid down by the Moon Com- 
mittee of the British Association, as the basis of the intended zone 
observations of the lunar surface, by the co-operative action of cer- 
tain English astronomers. The beautiful stereoscopic views of the 
moon, with which all are familiar, have done much, and are capable 
of doing more, in throwing light on the configuration of the lunar 
surface. It is especially the stereoscopic combinations of enlarged 
pictures which are calculated to impart a correct knowledge of the 
relative height and depressions of the terraces, undulations, dykes, 
and furrows of our satellite. 
In pursuing his favourite subject Mr. De la Rue has successfully 
taken pictures of Saturn, Jupiter, and Mars, and of some of the 
fixed stars. The most valuable, however, of Mr. De la Rue’s con- 
tributions to Astronomical Photography was the designing of the 
photo-heliograph of the Kew Observatory, and subsequently of the 
micrometer used for measuring the solar autographs, so as to bring 
them under the domain of calculation. 
Sir John Herschel suggested that it would conduce greatly to a 
true knowledge of our luminary if a daily photographic record of 
the sun’s surface were obtained. Acting upon this suggestion, and 
at the request of the Royal Society, Mr. De la Rue designed the 
Kew heliograph, which was erected at the Kew Observatory of the 
British Association in 1858, and has since that time been more or 
less worked. 
In 1860, this heliograph was taken to Spain, at the desire of 
the Royal Society, and was successfully employed by Mr. Dela Rue 
at Rivabellosa, in obtaining a series of pictures of the solar eclipse 
of July 18, before, during, and after total obscuration. 
In the Bakerian lecture, read before the Royal Society on the 
10th of April, 1862, the methods used in measuring these photo- 
graphs are fully set forth, and the results discussed at length.* 
From an early period several peculiar phenomena have been 
observed during eclipses of the sun, especially just before and after 
total obscuration. In 1783, Rydhenius, pastor of Forshem, states, 
“when the sun was about to lose his light, and also when he was 
about to recover it, he emitted rays that undulated like the aurora 
borealis and were of a fiery red colour.”+ Delisle has recorded an 
observation made in 1738 of the moon’s shadow passing upon a 
wall at the moment of total obscuration—tinged with different 
colours,t—by whom made we are not informed ; and in 1842 some 
French astronomers, according to Arago,§ observed similar pheno- 
* ¢ Philosophical Transactions for 1862,’ vol. clii., p. 333. 
t ‘ Acta Lit. et Scien. Succ.,’ tom. iv., p. 61. 
} ‘Memoires pour servir & |’Histoire et au Progres de l’Astronomie.’ St. 
Petersburg, 1738, 
§ ‘ Annuaire, 1846,’ p: 399. 
