and Astronomical Notices. 357 



and only the smoke shews any symptoms of the atmosphere being 

 otherwise than perfectly calm, the wheel is observed to have a slow 

 revolution. 



Altogether, therefore, Dr Robinson's anemometer may be con- 

 sidered to be the most perfect of any that have been brought for- 

 ward, and its results are most precise and valuable, and for station- 

 ary observations on land, hardly anything more can well be desired. 

 For travelling and nautical purposes, he Ims arranged a portable 

 form of the Edgeworthian hemispheres, which is almost identical 

 with one which I had contrived some years since for a naval friend, 

 Capt. Cockburn, R.N. ; and as a general notion seems to have pre- 

 vailed that no anemometer but Lind's can be used at sea, and that 

 the determinations must be far too rough to make the correction for 

 the motion of the ship of any moment, it may be interesting to 

 know that Capt. Cockburn, who has just returned from China, has 

 had my Edgeworthian anemometer in constant use for three years, 

 and that all the officers of the ship felt more and more confidence 

 in its indications the more that it was used, and the more accu- 

 rately that the correction for the motion of the vessel was applied, 

 according to the law of the parallelogram of forces. 



The chief difference between Dr Robinson's form and my own, is 

 that in his, the recording wheels, instead of being permanently con- 

 nected with the revolving spindle, are only brought into contact 

 with it by the finger, during such time as the observation is being 

 made ; a method which would certainly be very conformable to the 

 usual plans on which sailors observe the rate of the ship by the log 

 line, and therefore likely to be received with more favour, and 

 noted with more accuracy than any other. 



2. Hour of Observation for Mean Temperature.— The import- 

 ance of improving meteorological instruments for use at sea, can 

 hardly be estimated too highly, for there alone, can we expect 

 general laws to be found sensibly free from local irregularities ; and 

 every ship admits, with very little alteration, of being turned 

 into a peculiarly efficient observatory for such phenomena. This 

 has been recently insisted on by Mr S. M. Drach, who finds from 

 his own theoretical researches, as well as Mr Glaisher's observa- 

 tions and deductions, that the important element of the moan tem- 

 perature of the day can be satisfactorily and almost absolutely deter- 

 mined by four equidistant observations, whatever be the commencing 

 hour. He prefers, however, 5 and 11 a.m., and 5 and 11 p.m., and 

 in case of observations at sea, and in a uniformly moving ship, pro- 

 poses to refer the mean of those observations to the ship's place at 

 2 P.M. He further points out that if the thermometer be likewise 

 observed at 6 and 12 a.m., and 6 and 12 p.m.,, the horary increase 

 may also be well determined. 



3. Luminous Meteors and Aurorce. — As a transition subject be- 

 tween meteorology and astronomy, attention may be called to the 

 circulai's sent round by Professor Baden Powell, of Oxford, with 



