Z1^ 



NATURE 



[February 20, 1896 



by MM. M. Meslansand F. Girardet, the other by M. A. Colson. 

 In the first paper, the method previously used with success by 

 M. Meslans in the preparation of other organic fluorine deriva- 

 tives, the treatment of the corresponding chloride with metallic 

 fluorides, was employed. M. Colson used a rather different 

 method, the action of the halogen acid upon the organic acid in 

 presence of a dehydrating agent. With hydrogen fluoride, the 

 anhydride of the organic acid gives the best results ; thus with 

 acetic anhydride the reaction is 



(CUs-CO), O + IIF = CH3.CO.F + CH3.CO.OH. 

 The operation, which must be carried out in a freezing mixture in 

 a metallic flask, gives a theoretical yield. Acetyl fluoride boils 

 at 20° -8 under a pressure of 770 mm., and its density at 0° is 

 1-0369. Propionyl fluoride boils at 44°, and is lighter than 

 water, its density at 15° being about 0-972. Benzoyl fluoride, 

 which has already been prepared by M. Guenez, is best 

 obtained by acting with benzoyl chloride upon dry zinc 

 fluoride, and is a liquid of extremely irritating odour, boiling 

 at 154°. 



The additions to the Zoological Society's Gardens during the 

 past week include a Common Viper (Vipera bertis), British, 

 presented by Mr. S. Ockenden ; four Japanese Teal {Qiierqiie- 

 dula formosa, 6 6 9 9) from North-east Asia ; two Smews 

 {AfergHs albellus, 6 6), European, a Black Lark {Melanocorypha 

 yeltonensis) from Siberia, purchased ; a Purplish Death Adder 

 i^Pseudechis porphyriaca),2,V\xnc\x\\2A.QA Tree Snake [Dendrophis 

 piinctularid) from Australia, deposited ; a Hybrid Pheasant 

 Antelope (between Tragelaphtis grains, 6 , and Tragelaphiis 

 spekii, ? ), born in the Gardens. 



OUR ASTRONOMICAL COLUMN. 



Perrink's Comet. — A telegram from Kiel announces the 

 re-discovery of Perrine's comet by Dr. Lamp, on February 13. 

 At I7h. 40m., Kiel mean time, it was in R.A. igh. 44 "Sm. and 

 deck -2° 22'. The R.A. agrees well with the ephemeris 

 published in Nature on January 23, but the south declination 

 is about a degree greater than that predicted. 



A New Comet. — Another telegram from Kiel is as follows : 

 "New comet Perrine Lamp, February 15, i7h. 28"6m., Kiel 

 mean time; R.A. I9h. 26m. 44s., deck - 1° i' 56" ; daily 

 movement in R.A. 7m. 36s., in decHnation 2° 57' towards the 

 north ; bright." The new comet is thus in the immediate 

 neighbourhood of the original Perrine's comet, but it has a much 

 more rapid movement. Both comets are in the constellation 

 Aquila, rising about 4 a.m. 



The Zodiacal Light.— During the last three years the 

 zodiacal light has been very carefully observed by E. Marchand, 

 under the advantageous conditions afforded by the observatory 

 of the Pic du Midi, at an altitude of 2860 metres {Bull. Soc. AsL 

 de France, February). Ordinarily this phenomenon is best seen 

 during the evenings of spring or in the mornings of autumn ; 

 but in the absence of the moon, when the sky is clear, it is seen 

 at all times of the year from the mountain observatory, com- 

 pletely encircling the celestial sphere. The limits of the 

 luminosity have been plotted on charts, and taking the mean 

 positions of the boundaries, it is found that the width of the belt 

 of light is about 14°, and that it is very nearly a great circle 

 inclined 6° or 7° to the ecliptic, with a longitude of about 70° 

 for the ascending node. Now the inclination of the sun's 

 equator is about 7", and the longitude of the ascending node is 

 about 74° ; hence, it is concluded that the central plane of the 

 zodiacal light coincides with the plane of the sun's equator. 



The observations support the idea that the attenuated cosmical 

 matter of which the zodiacal light is probably composed extends 

 all round the sun, in the form of a very flattened ellipsoid of 

 revolution, to a distance well beyond the earth's orbit. 



In the part of the sky opposite to the sun, the brightness of 

 the light is not greater than that of the most feeble parts of the 

 Milky Way, but it becomes much more intense as the sun is 

 approached. The increase of brightness in the direction of the 



NO. 1373, VOL. 53] 



sun, however, is more rapid than can be accounted for mereljr 

 by the increased thickness observed, so that a greater condensa- 

 tion of cosmical matter in the neighbourhood of the sun seems- 

 probable. Near the horizon, the width of the zodiacal light 

 seems generally greater than that which traverses the sky ; but 

 It IS pointed out that this may be due to the same cause as that 

 which makes the sun, moon, or constellations appear larger 

 when near the horizon. The " Gegenschein," or counter-glow, 

 does not appear to have been noted. 



Surface Drift ok Jupiter.— A useful summary of the 

 various determinations of the rotation period of Jupiter in 

 different latitudes is given by Mr, Stanley Williams {Monthly 

 Notices, Ivi. No. 3). Nine distinct currents can certainly be 

 recognised, and their boundaries are pretty sharply defined, 

 though possibly varying slightly in position from time to time. 

 These currents, with the exception of that including the red 

 spot, completely encircle the planet, travelling due east and 

 west, and giving little or no indication of any movement towards 

 or from the poles. In the following tabular statement the 

 number of the zone or current is followed by the zenographical 

 latitudes of its boundaries ; then follows the average rotatioa 

 period of the zone expressed in time and in terms of the equa- 

 torial period. 



Period. 



There is a remarkable want of symmetry in most of the cur- 

 rents. In the northern hemisphere the drift is nearly uniform, 

 from the pole to lat. 28°, and there is nothing equivalent to the 

 red spot (zone VII.) ; in the southern hemisphere there is no- 

 counterpart of the region about lat. 25°, which is such a pro- 

 minent feature in the northern hemisphere. It is suggested that 

 atmospheric circulation in a north and south direction may take 

 place through the narrow rifts which have been seen to traverse- 

 obliquely some of the belts and clear zones. 



THE TEMPERATURE OF AIR AND THE 

 PROBLEM OF AN ICE AGE> 



T^HE mean temperature / of the air is determined by the balance 

 -*■ of radiations received from the sun and from the soil with that 

 given up towards the sky, and is ruled by the action of meteoro- 

 logical factors. According to Maurer's and Trabert's discussion 

 of nocturnal temperatures, air radiation in the atmosphere is a 

 linear function of its temperature ; so radiations from soil and 

 towards sky are expressed as proportional to the diff'erences 

 \kts - t), {t - tc)} of t from the mean temperature 4 of soil, and 

 from the mean temperature tc of an ideal stratum, the radiations 

 of which would be equivalent to that of the whole atmosphere 

 and of all the celestial bodies except the sun. This temperature 

 tc I call temperature of the sky. 



Similarly, the mean temperature tsoi soil is determined (if we 

 abstract from meteorological agents, that is in solar climate) by 

 the balance of its radiation towards the sky [which is propor- 

 tional to {t^ — /f)] with that fraction of mean solar heat which is 

 bestowed upon heating the surface considered. The mean annual 

 solar heat received by unity of surface at the limits of the 

 atmosphere (which is 0-305 of the solar constant at the equator) 

 diminishes with the latitude A, not as cos A, but, according to- 

 Wiener's computations,as the cosine of an auxiliary angle ^, which 

 is o°at the equator, and 65° 31' at the poles, and which repre- 



1 I beg f)ermission to briefly review the assumptions upon which Section 

 II., III. of "I e Cause deli' Era Glaciale " (Pavi.a, 1865) is based, and 

 which the reviewer of the book in Nature (No. 1348, vol. Hi. p. 4i2> 

 judged as far from satisfactory. — LuiGi De Marchi. 



