Feb. 4, 1875] 



NATURE 



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a similar recurrence of \n"c'ssitudes of climate may possibly be ' 

 detected in still earlier periods of the earth's historj-. These are ' 

 questions of the highest interest ; the forthcoming expedition I 

 may do much towards their solution, and it is to be hoped that j 

 those now directing the scientific arrargemenls will not neglect | 

 an opportunity of such rare occurrence. I 



There is noihing to be said against the appointment of a zoolo- 

 gist and botanist, provided geology be not neglected ; but if a 

 third addition to the scientific staff should be impracticable, it ' 

 would appear preferable that a good geologist should be in- , 

 structed to Icok after the fev^ small plants which may be added 

 to those already known, than that the opportunity should be lost 

 of throwing light on a subject which is acknowledged on all 

 hands to be shrouded in the greatest obscurity. 



Birmingham S.\MUEL Allport 



Upper Currents over Areas of Frost 



H.Wiys been for many years engaged in the discussion of 

 upper currents, I believe that I can contribute an item of infor- 

 mation towards the solution of the question asked by M. De 

 Fonvielle in N.WURE, vol. xi. p. 193. 



During many of the hardest frosts experienced in the West cf 

 Europe, moist southerly winds of mild temperature prevail on 

 the extreme western coasts of the British Isles, and occasionally 

 cf France and Portugal ; extensive areas of low pressure 

 existing on the North Atlantic, and of high over Western and 

 Central Europe ; isobars running nearly S. and N. , and gradients 

 being steepest in the W. Under these conditions, of'en per- 

 sistent for many days, cirrus-clouds travelalmnst invariably with 

 upper currents from points between S. and W. in the extreme 

 west, and commonly from poin's between S.W. and N.N.W". 

 over the whole western portion of the area of frost. 



A slight " backing " of the last-mentioned current is 

 com^nonTy one of the first local premonitions of the change of 

 weather, and may often be detected by the observer before any 

 apparent change has taken place in the atmosphere near the 

 earih's surface, and even when the frost is temporarily becoming 

 more intense. 



But this rule is not invariable. I have several examples in 

 which the upper current continued from N. or N.W. until the 

 thaw hid commenced ; and in those ins-ances the southerly 

 wind, at each station as it reached it, appeared to spring -a^ first 

 en tlu cartlts surfacf, and to be slowly communicated to the 

 higher regions of the atmosphere. 



And, on the other hand, the upper currents will occasionally 

 "back," even to S.W. or -S., when a local depression is advan- 

 cing in the S.W. and about to pass to the S. of the observer ; 

 when, instead of a thaw, a fall of snow and an increase of frost 

 will probably occur. Without the aid of telegraphic reports it 

 is almost impossible beforehand to distinguish this occurrence 

 from the advance of the general depression in the west 



On Jan. i, 1875, the cirrus travelled from S.W. in the west, 

 and from W. over England and France. Between this and the 

 surface-wind were intermediate currents from S. points, of con- 

 siderable velocity, and (as shown by the " silver thaw") of high 

 temperature. 



Jn frosts lil:e that of Jan. and Feb. 1S55, when the high pres- 

 sures are in the north, cirrus travels almost invariably from W. 

 or S. points over the area of frost. 



It is remarkable that in no instance are cirrus-currents from 

 easterly points accompanied by severe frost. 



On the subject of the general laws of the upper-cuirent circu- 

 lation I cannot here eiiter ; but I will mention, at the risk of a 

 slight egotism, one out of many proofs of the utility of their study. 

 Through the stormy summer of 1S72, being constantly questioned 

 by neighbours as to the probable coming weather, 1 posted a 

 daily weather forecast on my door. In no instance did this prove 

 incorrect, even as to the hour of a coming thunderstorm. And 

 in all instances these forecasts were frituipcdly based on calcu- 

 lations derived from the observation of those upper currents which 

 " weather prophets," et hoc genus omne, almost universally 

 neglect. W. Clement Ley 



Ashby Parva, Lutterworth, Jan. 20 



Deccmpcsition of Iron Pyiites 



The "curious phenomenon" described by Mr. Krederic Case 



(Nature, vol. xi. p. 249) is by no means an uncommon one. 



It is due to oxidation, and the conversion of a portion of the 



pyrites into soluble sulphate of iron. This Jecompusiti n is 



much aided by the presence of moisture ; it is very doubt(ul 

 whether it would occur at all in a dry atmosphere, and I suspect 

 that the particular case in the Maidstone Museum, where tie 

 pyrites has thus crumbled, is near an outside wall, or otherwise 

 exposed to humid influences. I have seen large heaps of pvrites 

 thus decomposoig at the foot of the troughs where coal-slack is 

 washed beiore converting it into coke. The sulphate of iron 

 used in the manufacture of Xordhausen sulphuric acid is com- 

 monly obtained by similar oxidation of pyrites, which is aided 

 and economised in this case by previously roasting away a poi tion 

 of the sulphur. 



Mr. Case may easily test the above explanation by placing 

 some of the crumbled pyrites in a small quantity of water, leaving 

 it Uiere for an hour or tno, then filtering through blotting piper 

 and evaporating the clear filtrate slowly to dr)nes5. If I am 

 right, he will find a resdue of small crystals of sulpha'e of iron. 

 A few drops on a strip cf glass will be sufficient to show these 

 cr)-stals, if magnifying power is used : or the presence cf a 

 soluble salt of iron may be shown by adding a little feno-cysnide 

 of potassium to this filtered liquid. 



W. Mattieu Williams 



With reference to a statcme-t and inquiry put forth last week 

 in your columns by Mr. Frederic Case, of Alaidstone, respecting 

 the decomposition of some iron pyrites, I beg to state that pre- 

 cisely the same effect took place with similar specimens exhibited 

 in our museum many years ago. The cause is due, I understand, 

 to the influence of air and moisture forming ferrous sulj^hate 

 (green vitriol or copperas). In our case this salt appeared in 

 abundant crystals, and was suflSciently strong to partially oblite- 

 rate and destroy a contiguous manuscript. 



Alnwick Mechanics' Institute Geo. Lingwood 



O.v p. 249, vol. xi. k a query by Jlr. F. Case as to the 

 spontaneous decomposition of iron p)Tites. I would suggest 

 that the sulphur and iron of the mineral have been oxidised at 

 the exper.se of the oxygen of the atmosphere in the presence of 

 moisture. Some years ago I collected specimens of fossil wood, 

 &c., from the London clay found in a deep well at the corner of 

 Colchester Garrison. After a time my specimens were crumbiim- 

 to powder, and were coiered with light, silky crystals, which 

 upon analysis proved to be sulphate of iron. Upon examining 

 the clay minutely it was found to contain numerous gclden 

 spangles, exceedingly small, of native sulphuret of iron or iron 

 pyrites, and the conclusion arrived at was that these spanqles 

 had absorbed o.xygen and produced the crystals, and also ren- 

 dered the specimens friable. A. P. Wire 



Dunstable 



OUR ASTRONOMICAL COLUMN 

 Varl\ble Stars. — (i). On the 19th of June, 1S23, 

 during the visibility of Enckes comet in the southern 

 hemisphere, Riimker, who was then at Paramatta, 

 X.S.W., compared the comet with a star which he judged 

 to be between the fourth and fifth magnitude, but could 

 not find in any of the catalogues. The sun set at 

 Paramatta on this evening at 4h. 58.11., and the comet 

 was observed from 6h. 3m. to 6h. 46m. mean times, 

 or from an altitude of 20' to 11°. An experienced 

 observer as Riimker then was would net be likely to 

 make any great error under these circumstances in esti- 

 mating the magnitude of his comparison-star. Gibers 

 in July 1824 first directed attention to it, as probably a 

 remarkable variable star. He noted its occurrence in 

 Harding's Chart as a seventh magnitude, and supposed it 

 was inserted from an observation by that astronomer, who, 

 as is well known, conipared his maps with the sky ; and 

 further, he pointed out that it had been observed by 

 Bessel in his sixty-third Zone, 1822, March 14, and then 

 estimated also of the seventh magnitude. Riimker deter- 

 mined the position of his uncatalogued star, by reference 

 to three neighbouring ones found in the " Histoire 

 Celeste,"' and it agrees almost precisely with that given 

 by Bessel's Zone. This object is No. 134 in Santini's 

 Catalogue (Deck — 2"), where it is again estimated a 

 seventh magnitude. It does not occur in Argelanucr's 



