May ii, 1882] 



NA TURE 



3i 



and working at the same speed, the motion to the one hand will 

 produce red, and when reversed, blue? Mr. Hannay also 

 seems to imply that the colours of my experiments to be seen 

 well, should be looked at passively or without keen attention. 

 On the contrary, the more light thrown on them, and the keener, 

 fresher, and younger the eyes of the observer, the more brilliant 

 are the colours, and if a boy of ten or t« elve years old, who 

 never saw anything of the sort before, be called in, he will 

 describe them letter than grown people. 



Scientific men have hitherto considered it a sufficient explana- 

 tion of these experiments to say the effects are " physiological," 

 as if colour were ever anything else. Newton says, speaking of 

 coloured rays, that he uses the term merely to suit the under- 

 standing of the vulgar, as they are nothing but a certain power 

 and disposition to stir up a sensation of this or that colour. 

 Prof. Ogden Rood again classes these as subjective colours, a 

 word which, if it has any meaning at all beyond a very limited 

 one, can have none with reference to colours which remain per- 

 manent so long as the machine is in motion. 



27, York Place, Manchester, April 22 Naher Smith 



How may Clouds consisting of Liquid or of Frozen 

 Water be Distinguished ? 



In Nature, vol. xxv. p. 529, M. de Fonvielle asks my 

 opinion as to what observations may be made in a balloon to 

 discover whether in a cloud whose temperature is below zero the 

 minute particles of water are liquid or solid. 



There may be difficulties in the way of deciding by direct 

 observation of the form of the particles, whether they are globules 

 or crystals. But since H. B. de Saussure, a century ago (" Essai 

 sur l'Hygrornetrie), by means of a single lens, could distinguish 

 in the air over heated water, globules of condensed water of 

 different size, greater ones which appeared to him full, and 

 smaller ones which he regarded as hollow; and when in more 

 recent times A. Waller (Philosoph. Transactions, 1847) could 

 make his " microscopic observations on the so-called vesicular 

 vapour of water as existing in the vapours of steam and in clouds, 

 &c," with the result that he denied the existence of mist-vesicles, 

 it seems possible that by means of a magnifying instrument the 

 form of the particles suspended in the air can be recognised. 



A sure evidence, but obtainable only under favourable circum- 

 stances, that the particles forming a cloud are ice-crystals would 

 be the observation of the halos of 22 and 46 radius and of para- 

 helions as produced by the cloud. Hermann Kopp 



Heidelberg, May 3 



On the Conservation of Solar Energy 



Dr. Siemens's theory of the constitution of the sun implies that 

 there is an absorption of solar rays constantly going on in space. 

 If this is so, space cannot be perfectly transparent. 



An astronomer of the early part of the present century — I 

 think it was Olbers — came to the same conclusion, though from 

 different reasons. He found that as the space-penetrating 

 powers of the telescope is increased, the number of stars lliat 

 become visible does not increase so rapidly as it would if they 

 were evenly scattered through space, and if space were perfectly 

 transparent ; and he concluded that most probably space is not 

 perfectly transparent. This, how ever, is by no means conclusive, 

 because it is possible that the reason why the number of stars 

 that become visible does not increase as it ought to do on the 

 supposition, is that the number of stars in the universe is limited. 

 Joseph John Murthy 



Old Forge Dunmurry, co. Antrim, May 3 



CYCLONES 1 

 II. 

 T N our former article we dwelt on the deductions arrived 

 *■ at by the author from a consideration of the mecha- 

 nical theory of cyclones. We will now proceed to examine 

 how far such theoretical relations are corroborated by the 

 results of observation. The results of observation utilised 

 by the author comprise those of the Rev. W. Clement 

 Ley, published in his "Laws of the Winds"; those of 



1 "Methods and Results of Meteorological Researches for the use of the 

 Coast Pilot." Part II. — On Cyclones, Waterspouts, and Tornadoes. By 

 William Ferrel. (Washington, 1880.) Continued from p. 12. 



Prof. Loomis, deduced from a study of the U.S. Signal 

 Service charts ; those of Dr. Hildebrandsson, with re- 

 gard to the upper currents from an examination of the 

 Danish synoptic charts ; those of Capt. Toynbee, from 

 a study of the Atlantic storms ; and lastly, some con- 

 tained in a recent work on the hurricanes of the 

 Antilles, by Padre Vines of Habana. Mr. Ferrel at the 

 outset pointedly remarks that for a mariner to be able 

 to make use of the laws deduced from a study of the 

 theory of cyclones, not only a knowledge of such laws is 

 requisite, " but likewise of the normal states of the wind 

 and of the barometric pressure in all parts of the ocean 

 and at all seasons of the year, unaffected by the abnormal 

 disturbances of these progressive cyclones ; since with 

 a knowledge of the normal conditions of the winds and 

 of the barometric pressure at any time and place he can 

 perceive the first indications of the abnormal disturbances 

 which are the forerunners of these storm?, and so can be 

 on his guard, and then with a knowledge of these storms 

 or cyclones, he can generally avoid at least their most 

 dangerous part." 



With regard to the first result from theory, viz. the 

 general incurvature of the winds in a cyclone, which was 

 formerly altogether denied by the cyclonists — so-called — 

 Reid and Piddington (not Redfield), or inordinately mag- 

 nified in every case by Espy, and other upholders of the 

 radial theory, there seems to be no doubt from the results 

 of observation here given, as well as from others not cited 

 by the author, that the wind deviates to a considerable 

 extent from the tangent to the isobars inwards towards 

 the low centre. Moreover, in accordance with theory, this 

 inclination is greater at inland stations where there is 

 more surface friction than at or near the sea when it is 

 less. Thus Ley found the inclination to be about 29° for 

 inland stations, but only i3°for those on the coast. This 

 difference between the inclination at sea and on land may 

 perhaps account for the tenacity with which sea captains 

 still cling to the notion that the wind blows in circles 

 coincident with the isobars : since it is precisely at sea 

 where the incurvature should theoretically be least. The 

 increase in the inclination corresponding to a decrease in 

 the latitude is likewise borne out by observation. Thus 

 from Ley's observations, which embrace North and South 

 Europe, the mean inclination to the isobar is about 25°, 

 from those of Capt. Toynbee on latitude 50 it is 29 , from 

 those of Loomis nearer the equator in America 47°, I t from 

 those of Padre Vines in the Antilles 45 , and we may add 

 from some in the Bay of Bengal, mentioned by Blanford, 

 about 42°. 



It is thus pretty evident, as the author remarks, that 

 "though the horn-cards of Piddington based on the 

 strictly circular theory of the winds may still be used at 

 sea in high latitudes without great error, yet nearer the 

 equator they must become more erroneous, and entirely 

 fail at the equator if cyclones could exist there." Mr. 

 Meldrum, of Mauritius, as far back as 1867 drew atten- 

 tion to the disasters which resulted in consequence of 

 vessels having estimated the direction of the centres of 

 cyclones according to the rules of the circular theory, 

 and since the publication by M. Faye of his " Defense de 

 la loi de tempetes," has strenuously opposed the resusci- 

 tation of this exploded doctrine. He has also lately 

 given an admirable proof of the truth of the incurvature, 

 by publicly announcing when the wind, in a cyclone on 

 March 21, 1878, was from the north-east in Mauritius, 

 that the centre of the storm was not to the north-west- 

 ward according to the circular theory, but to the west- 

 south-westward, which was afterwards found to have been 

 the case. 



It is a manifest duty therefore which mankind owes itself, 

 if the dangers of the sea are to be minimised, that the 

 amount of inclination of the wind to the isobar should 

 be determined by observation in different seas and for 



' Some of these included very gentle winds. 



