532 



NA TURE 



[April 9, 1885 



,£1,500 and a Krupp 91-inch B.L. gun of 14J tons costing 

 ;£3>453> the length of the former was i25'5 inches and 

 that of the latter 157-6 inches. Great complaints were 

 justly made of the unfairness of the comparative trial, be- 

 cause, while the English gun was strictly confined to 

 service conditions, the German gun was repaired and 

 altered so that every feature of the original combination 

 was changed. After some months' delay Krupp raised 

 the initial velocity of his gun from r , 1 1 S '3 f.s. to 1,286 or 

 1,414 f.s., according to whether a 336 lb. shot or a 275 lb. 

 shell was used. Time has now decided this contest. 

 Here we remark how ready Krupp's party were to notice 

 defects and apply remedies. If the English party were 

 debarred from effecting improvements at Tegel, they were 

 free to improve at home. They had seen that it was 

 possible to construct a 9Hnch B.L. gun, firing lead-coated 

 projectiles, which could compete with an English 9-inch 

 M.L. gun. But we do not hear of any further attempts 

 having been made to render the no-pounder (about 7 

 inch) B.L. Armstrong gun an efficient weapon. 



Last spring we were informed by authority that the new 

 B.L. gun then about to be constructed would be double 

 the length of the old B.L. gun. And quite recently the 

 Times intimates a doubt about some newly constructed 

 guns having sufficient strength in front of the trunnions to 

 resist the full charge for which they were constructed. 

 Now some years ago we heard a good deal about the 

 doings of a Committee on Explosives, which carried on 

 experiments for several years, and at last reported. What 

 could be the use of such a committee if it did not furnish 

 rules tar properly proportioning the strength of guns, and 

 for determining the proper length of bore required for the 

 profitable consumption of charges of slow-burning powder? 

 Although Rodman and the pressure gauges and chrono- 

 scopes appear to have failed to give reliable results, it 

 would not be difficult to contrive experiments which would 

 give the practical value of every inch in length of the bore, 

 and at the same time show the effect of great length of 

 bore upon the steadiness of the motion of the elongated 

 projectile. 



In October, 1SS3, it was stated in the papers that some 

 comparative trials had been made at Portsmouth before 

 " my lords," between a Krupp and an English 6-inch B.L. 

 gun, " greatly to the advantage of the former." A Krupp 

 gun fired a 64 lb. shot with a 14 lb. charge and the English 

 gun a 100 lb. shot with a 34 lb. charge. That is, the 

 charge of the Krupp gun was two- ninths, and that of the 

 English gun three-ninths of the weight of its shot. This 

 increased charge might be a positive disadvantage to the 

 English gun if it was a short one. This is a case requiring 

 the most careful and candid investigation. Any fine 

 morning a thorough comparison of the performances of 

 these two guns might be carried out in a searching man- 

 ner, if only known means of doing this were employed. 

 In order to succeed in gun-making"it is absolutely neces- 

 sary tor careful experiments to be carried out to clear up 

 anomalies, such as we have mentioned. 



This work is illustrated by seventy-eight most carefully 

 executed plates of guns, carriages, large steam hammers, 

 and cranes, furnaces, plans of works, &c, and it concludes 

 with estimates of the expenses of equipping a gun foundry 

 according to modern requirements. F. B. 



ON THE FORMATION OF SNOW CRYSTALS 

 FROM FOG ON BEN NT ITS 



T N addition to the actual fall of snow, hail, &c, there is 

 on Ben Nevis a form of solid precipitation scarcely 

 known on lower ground, but of almost daily occurrence 

 here. In ordinary weather the top of the hill is enveloped 

 in drifting fog, and when the temperature of the air and 

 ground is below freezing this fog deposits small crystalline 

 particles of ice on every surface that obstructs its passage. 



These particles on a wall or large sloping surface, so well 

 described in a recent letter in Nature (vol. xxxi. p. 216), 

 combine to form long feathery crystals ; but on a post or 

 similar small body they take a shape more like fir-cones, 

 with the point to windward. Whether this deposition is 

 from the vapour of the fog directly or from actual particles 

 of frozen water carried along in it is not very clear. The 

 forms and arrangements of the crystals vary according to 

 the form of the surface to which they adhere, but all 

 belong to this feathery or cone type, the branches lying 

 at an angle of 30° with the main axis pointing to wind- 

 ward. They are formed wherever the wind blows past 

 an obstructing body. On a flat board they gather first 

 and most abundantly near its edges, forming a most 

 beautiful border around it ; while the centre, which I sup- 

 pose the wind does not directly reach, remains clear. A 

 round post, on the contrary, has an almost uniform crop 

 of these crystals all over its windward half, and so accu- 

 rately do they point to windward that it is possible to 

 trace changes in the direction of the wind from the 

 successive layers of crystals lying at different angles. 

 The rate of growth varies with the density of the fog and 

 the speed of the wind, but for the ordinary winds and 

 fogs of this exposed position about half an inch per hour 

 may be taken as a rough average. I have never seen it 

 exceed two inches per hour. If there is a damp feeling 

 in the air, if in fact it is mist that is passing rather than 

 fog, the crystals are icy and hard ; but when the tem- 

 perature is well below freezing and the fog feels compara- 

 tively dry, they are looser in texture, seem when first 

 formed to be attached by a mere point to whatever they 

 are on, and are pretty easily knocked off. There is prac- 

 tically no limit to their growth ; last winter during a long 

 continuance of strong south-westerly winds and cold 

 weather a post 4 inches square grew into a slab of snow 

 some 5 feet broad and 1 foot thick in less than a week, the 

 crystalline mass then fell off by its own weight and a new 

 set began to form. 



The effect of this growth on all the instruments exposed 

 to its action may be easily imagined. Nothing keeps its 

 shape or colour. The louvres of the Stevenson's screen 

 for the thermometers become serrated with rows of teeth 

 which quickly coalesce into a solid mass completely 

 stopping any circulation of air inside the box. The use 

 of exposed radiation thermometers, black bulb in vacuo, 

 &c, is rendered well nigh impossible, as these delicate 

 glass instruments would run serious risk of breakage in 

 clearing them of the deposit, while their readings would 

 have little value, being merely the record of the tem- 

 perature inside a more or less opaque mass of snow 

 Very often the rain-gauge is coated with these crystals 

 an inch thick on its windward side, while not a particle 

 is to be seen inside. Ordinary anemometers of the type 

 of Dr. Robinson's cup instrument become useless ; the 

 cups are no longer hemispheres, but irregular hollow 

 bodies bristling all over with pointed crystals, and the 

 arms carrying them increase to many times their original 

 thickness, thus offering much greater surface for the wind to 

 act on. Under such circumstances the anemometer at the 

 Observatory is usually left to its own devices, and grows into 

 an irregular mass of snow scarcely showing any trace of 

 its original outline, to be cleared again when dry weather 

 or a thaw gives it a chance of working. When the fog 

 comes on while the anemometer is still turning, the crys- 

 tals form chiefly on the outside of the cups and around 

 their edges, leaving the insides pretty clear. The arms 

 carrying the cups get completely covered, and on the 

 diagonal stays supporting the arms the crystals show a 

 beautiful "twined" structure pointing downwards and 

 outwards on each side. 



Occasionally the crystals are smokey-brown in colour 

 instead of white. For example, those found on December 

 23, [884, were distinctly brown, but on the 24th these 

 were overlaid by a pure white set. What causes this 



