Dec. 13, 1888] 



NATURf: 



49 



of the base was nearly three- sixteenths of an inch, while the 

 shorter basal diameter was about a sixteenth less. Of course, 

 the above measurements are merely general, and were necessarily 

 taken in a rather rough fashion. 



The figures i, 2, 3 below, although diagrammatic, will give a 

 better idea of the usual shape of the hailstones than could be 

 readily furnished by any further detailed description. 



When sixteen hailstones, all of which were practically of the 

 same size, were placed closely together side by side, so that all 

 their apices terminated at the same point, a half spheroid was 

 constructed, the curved basal surfaces of the pellets running 

 neatly into one another to form the external globular surface. It 



Fig. I.— Magnified. Fig. 2.— Magnified. Fig. 3— Basal view ; 



magnified. 



is evident, therefore, that those particular hailstones, at least, 

 were originally portions of spheroids, each hailstone being a 

 segment (the i/32nd in this case) of a globe. How the icy 

 globes were formed, and what was the cause of their breaking 

 up into segments, are problems, I believe, that yet await serious 

 investigation. 



When the substance of any of the hailstones was observed 

 closely by means of a lens magnifying four times, it was seen to 

 be a transparent mass of ice, and fairly homogeneous in texture, 

 having apparently little or none of the fibrous structure which 

 has been previously noticed in other cases, and recorded by my- 

 self and other observers (see Nature, vol. xxxv. pp. 413, 438, 



Fig. 4.— Showing numerous liquid cavities in a hailstone ; magnified 

 six times. 



536). Each icy mass, however, contained scattered about in its 

 substance numerous small cavities, round, oval, or elliptical in 

 firm, which were filled wholly or partially with water (see 

 Fig- 4). 



In some cases these liquid cavities were so numerous and so 

 crowded together as to interfere seriously with the diaphaneity of 

 the hailstone and to give it quite a clouded or granulated appear- 

 ance. I may add that the convex basal surfaces of the hailstones 

 were not quite smooth and glassy, but exhibited a rather grainy 

 appearance, and were slightly but distinctly rough to the feel. 

 Alexander Johnstone. 



Edinburgh University, November 29. 



The Renaissance of British Mineralogy. 



The following passage occurs on p. 116 of Nature of 

 November 29, in an article on the above subject : — 



" Crystallography should be taught as a special subject ; and 

 a knowledge of it should be required not only of the mineralogist 

 but of the chemist, and even of the physicist. Hitherto, at least, 

 the chemists of this country have been too content either to leave 

 the crystalline forms of their artificial products undetermined, or 

 to impose the task of their determination on the already 

 sufficiently occupied mineralogist. It seems obvious, that in a 

 satisfactory system of education every chemist should be taught 

 how to measure and describe the crystalline characters of the 

 products which it is his fate to call into existence. On various 

 occasions expression has been given to this view, but the only 

 chemist who has yet seen his way to act upon it is Prof Henry 

 Armstrong, who I am happy to say, has introduced the subject 

 into the educational course of the City and Guilds Technical 

 Institute. I trust that before another generation passes away 

 his excellent example will be followed throughout the country. 

 A knowledge of the elements of crystallography, including the 

 mechanics of crystal measurement, ought to be made a sine qua 

 lion for a degree in chemistry at every University." 



The views thus expressed are shared by many chemists, and are, 



I believe, generally known. It is, however, not exactly correct 

 that "the only chemist who has seen his way to act upon it is 

 Prof. Henry Armstrong." 



Long before the City and Guilds Institute was established or 

 thought of, mineralogy, including crystallography, was a part of 

 the curriculum in the Department of Engineering and Applied 

 Science in King's College, London. ■\ 



Until the year 1879, mineralogy and crystallography were 

 studied in the Royal College of Science, Dublin, by students in 

 the Faculty of Mining only, but at my suggestion these subjects 

 mere made compulsory on the students in all Faculties. 



Furthermore, this subject was introduced into the course pur- 

 sued in this' College by the candidates for the Associateship of 

 the Institute of Chemistry, the Council of the Institute accepting 

 attendance at the course of mineralogy as equivalent to an equal 

 number of hours in the chemical laboratory. This arrangement 

 was carried out in 1881. It will be seen that mineralogy and 

 crystallography are subjects which have by no means been 

 neglected by chemists, though it is quite true that, like many 

 other science subjects, they have not taken their proper places at 

 the Universities. To chemists generally, there are without doubt 

 more important subjects of study than crystallography which are 

 not adequately taught ; I refer to the use of the microscope, 

 polarimeter, and spectroscope. These instruments are employed, 

 and are absolutely indispensable, in certain methods of chemical 

 analysis and research. 



In how few laboratories are any accurate measurements of 

 spectra made, or is the spectroscope used for any other observa- 

 tions than for detecting the alkalies and alkaline earths ! 



We have as yet no Professor of Spectrum Analysis, though it is 

 undoubtedly a fit subject for a distinct Professorship, and this fact 

 has, I believe, been recognized in Germany. If the advances in 

 chemistry made respectively by students of crystallography and of 

 spectroscopy be compared, it will appear that we owe very much 

 more to the latter than to the former. W. N. Hartley. 



Royal College of Science, Dublin, December I. 



" Weather Charts and Storm Warnings." 



I have just been reading Mr. Allan Broun's review of 

 Mr. Robert H. Scott's " Weather Charts and Storm Warnings," 

 in Nature, vol. xiv. p. 566, and note that the reviewer 

 says : — 



"Why, in all the disquisitions on fluid equilibrium, are the 

 constant low (barometric) pressures in the Antarctic regions south 

 of 60" neglected? Haw shall we account for the permanent de- 

 pression in the neighbourhood of Iceland referred to by the 

 author (p. 64) ? And, to come to our own country, how will 

 cyclonic winds explain the fact that the pressure of the atmo- 

 sphere diminishes, on the average of the whole year, at the rate 

 of one-tenth of an incti of mercury for 4° of latitude as we 

 proceed northwards ? " 



I have no suggestion to offer respecting the depression near 

 Iceland, but the other two — the depression about the South 

 Pole, and the diminution of pressure going northwards in Great 

 Britain— are parts of one general fact — namely, the diminution of 

 pressure in going from about lat. 30° to either Pole, which, how- 

 ever, is most marked in the southern hemisphere. This, 1 think, 

 admits of a simple explanation. The zones on each side of the 

 equator are occupied by the trade-winds, blowing from the east : 

 their cause is too well known to need statement here. But, by the 

 law of reaction, they necessitate the existence of winds of equal 

 total force from the west, and those west winds are formed in the 

 regions between the trade-winds and the Poles. Winds blowing 

 continuously round the Poles, in the same direction as the earth's 

 rotation, constitute vortexes, and the pressure at the bottom of 

 the vortex — that is to say, at the earth's surface — necessarily 

 diminishes towards the centre — that is to say, towards each Pole. 

 The diminution of pressure towards the Pole is much greater in 

 the southern than in the northern hemisphere, because in the 

 latter the unefjual heating of continents and oceans produces 

 currents of wind which, though on a large scale, are local 

 currents in respect to the entire hemisphere, and tend to break 

 up the vortex. 



The cause I have assigned is a vera causa — that is to say, it is 

 known to exist, and its effect must be of the nature of the effect 

 actually found. Perhaps some of your mathematical corre- 

 spondents will discuss the question whether it is of sufficient 

 magnitude to account for the effect. 



Belfast, December 2. JOSEPH JoHN MURPHY. 



