158 Notes and Memoranda. 



Notts, 310 inches fell in 2J hours, we can recall no rains more 

 noteworthy than those which have lately fallen." Mr. Symon 

 adds, "the facts appears to show that the heaviest fall was an 

 excessively local one of about five inches, extending along the north 

 side of the North Downs from Farningham nearly to Sittingbourne ; 

 Rochester, Chatham, and Strood, being on the northern limit of 

 excessive fall. It was accompanied by a violent thunder-storm, 

 which was most severe between Faversham and Canterbury ; thirty- 

 two sheep were killed by lightning near the latter city. About the 

 same hour it was raining very heavily at Deptford and Greenwich, 

 where about four inches of rain fell. Nearly four inches fell at 

 Billericay, in Essex." Mr. Symon's also informs us that nearly 

 twice as much rain fell at Deptford as at Camden Town ; and he 

 notes other cases in which the variation was similar between places 

 only a few miles off. Amongst the correspondence to the " Meteoro- 

 logical Magazine," Mr. Blackmore, of Teddington, remarks, that 

 the storm of the 26th was prenotified by the remarkable appearance 

 of the sky on the evening of the 24th, when the south-east sky 

 exhibited " a beautiful fan of blue divergent radii rising 30° above 

 the horizon, streaking across the redness like a windmill with blue 

 sails to it." Mr. Symon says that a friend sent him a sketch of a 

 similar appearance seen in Kentish Town on the 25th. 



NOTES AND MEMORANDA. 



Yekipication' op Sextants. — It is a disgrace to the mercantile marine that 

 the majority of the sextants with which their captains are supplied, and on which 

 their safe navigation often depends, are of the most worthless description. First- 

 class opticians, of course, supply reliable instruments, but ordinary sextant 

 mating has sunk so low as to resemble the worst sort of tailors' slop-work, and 

 the operatives engaged in this wretched business are miserably paid. The British 

 Association Observatory at Eew supplies the means of curing this evil, by testing 

 the instruments, and the apparatus now employed for this purpose, designed and 

 constructed by Mr. F. Cooke, is described in the " Proc. Eoy. Soc," No. 94. 



Experiments WITH the Eioid SrECTEOSCOPE. — Some time ago, we described 

 the general construction of the rigid spectroscope, made by Mr. Browning for 

 Mr. Gassiot, in order to test a suggestion of Mr. Balfour Stewart, that the position 

 of spectrum hues might be slightly affected by changes in terrestrial attraction 

 consequent on approaching to or receding from the poles. The instrument was 

 sent out in the surveying-ship " Nassau," and Mr. G-assiot has recently communi- 

 cated to the Boyal Society the report of Captain Mayne, together with remarks 

 thereon by Prof. Stokes and Mr. Balfour Stewart. The report says that the 

 micrometric reading increased as the barometer fell, and vice versa; it was also 

 affected by temperature. After deducting all other ascertainable sources of 

 change, it seems as if the difference of the earth's attraction between lat. 45° and 

 the equator may change the readings for the yellow of the spectrum to an extent 

 equal to about J of the interval of the D lines. Prof. Stokes thinks this slight 

 change may arise from other causes than difference in gravitation; and Mr. 

 Stewart, though regarding it as arising from that source, does not consider the 

 experiments conclusive. Farther information is therefore looked for with much 

 interest, as, when stripped from technicalities, the question to be decided is, 



