176 Scientific Intelligence — Optics, $c. 



On the 16th, 2h 50' sidereal time, it is north, following r Gemini abont 

 12' 30" in AR in time, and about 6' 40" north of the star. This observa- 

 tion was made by the equatorial instrument, and is not to be depended on 

 to great accuracy. 



On the 17th August, at 3 h 9' 55", the comet followed t Gemini 

 = 19' 26" in time, and south of the star, as 8' 27" 36, bar. 30.300, ther. 

 35°. This observation was made within two degrees of the horizon. I ob- 

 served t Gemini, and waited till the comet passed through the field. 

 Comet very faint. 



I searched diligently for it coming out from the sun, but could not find 

 it. — Letter from Mr Bunlop to Sir Thomas Brisbane. 



optics. 



6. Nature of the light emitted by lime, in a high state of incandescence. 

 Mr Herschel upon examining the light from lime obtained by Lieutenant 

 Drummond, and described in No. x. p. 319, found that it contains all the 

 usual rays, and three of those remarkable in quantity and quality, viz. 

 the red, the yellow, and the green. The red is intermediate between the 

 red and orange of the solar spectrum, but is nearer to the latter. It is re- 

 markable, as Mr Herschel mentions, that a red of the above character is 

 yielded by lime itself, whilst the colour given to burning bodies by the 

 combinations of that earth is a brick red. 



7. On the light developed at the separation of Boracic Acid into frag" 

 ments. — M. Dumas has observed that the boracic acid, when melted, pre- 

 sents a particular phenomenon at the moment of its cooling. When it is 

 cooled in a platina dish, at the instant when the contractions of the two 

 substances becomes unequal, the boracic acid splits and discharges a bright 

 light, which follows the direction of the cracks. This light, which is pro- 

 bably owing to the cause which developes the opposite electricities in plates 

 of mica quickly separated, is sufficiently strong to be seen in the day-time. 

 The experiment is a remarkable one in the dark. — Ann. de Chim. p. 324, 

 335. 



HYDRODYNAMICS. 



8. On the Periodical Fountain of the Jura, called the Round Foun- 

 tain, — On the 26th June 1826, M. Dutrochet read a memoir on this foun- 

 tain to the Academy of Sciences. This fountain is periodical, and not in- 

 termitting. The quantity of water which it discharges increases every 

 three minutes, so that the entire period is six minutes. The general ex- 

 planation given of these fountains is, that they are supplied by subterra- 

 nean reservoirs communicating with one another by channels which per- 

 form the office of syphons. This explanation, however, M. Dutrochet 

 conceives to be inapplicable to the round fountain. Here, indeed, the time 

 of the period is not constant, as the period is sometimes four minutes in 

 place of six, viz. two minutes of intermittence, and two of increase. Oh 

 the hypothesis of a syphon, the time of intefmittence ought to have no 

 influence- 



M. Dutrochet is of opinion that the periodicity, and all the phenomena 



