Page:Proceedings of the Royal Society of London Vol 2.djvu/97

Rh entering into intimate union with the oxide of platinum, produces fulminating platinum. The theories invented by Bergmann and Berthollet, to explain the detonation of fulminating gold, are satisfactorily applicable to the phenomena presented by the compound now described, the explosive powers of which may be referred to the sudden extrication of nitrogen, ammonia, and aqueous vapour.

Dr. Brinkley, of the Observatory of Dublin, having noticed for several years past a periodical deviation of several fixed stars from their mean places, strongly indicating the existence in them of annual parallax, the author was induced to institute a series of observations upon the subject, the results of which are submitted to the Royal Society in the present communication. Being unable to devote the mural circle, erected at the Royal Observatory in 1812, entirely to this investigation, the Astronomer Royal employed two ten-feet telescopes, fixed to stone piers, and directed to the particular stars whose parallax was suspected, and furnished with micrometers for the purpose of comparing them with other stars passing through the same field. The question of parallax is, theoretically speaking, rather curious than important; but with regard to the state of practical astronomy the case is very different, and, as far as relates to the natural history of the sidereal system, it is a subject of interest to ascertain whether the distances of the nearest fixed stars can be numerically expressed from satisfactory data, or whether it be so immeasurably great as to exceed all human powers either to conceive or determine.

The principal stars observed by Dr. Brinkley were, α Lyræ, α Aquilæ, α Cygni.

The mean of forty observations of α Lyræ, made by the Astronomer Royal between June 22 and August 21, gave for the north polar distance of that star 51° 23′ 0″·278. The mean of twenty observations nearer the period of opposition gave 51° 23′ 0″·468. The mean of thirty winter observations is 51° 23′ 0′·872. The discordance, therefore, between the winter and summer observations does not exceed 0″·6, which is only one third the discordance observed by Dr. Brinkley.

With α Cygni the total discordance in favour of parallax was 0°·556; also only one third that observed by Dr. Brinkley; and with α Aquilæ it is less than 0″·5, equal only to one fourth of the discordance observed by Dr. Brinkley.

From these and other observations detailed in the paper, the Astronomer Royal observes, that in the three stars supposed by Dr. Brinkley to have the greatest parallax, the discordance between the summer and winter observations is not less than 0″·5, and scarcely exceeds 0″·75: and that although these quantities are much less Rh