September i6, 1909] 



NATURE 



335 



LETTERS TO THE EDITOR. 

 [The Editoi docs not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part o/ Nature. 

 No notice is taken of anonymous communications.] 



The Summer Season of igog. 

 In endeavouring to estimate the character of a coming 

 season, the following method is, I think, often serviceable, 

 i^et us take, as a concrete case, the annual numbers of 

 very hot days at Greenwich (80° or more) from 1841 to 

 1908. Add these in the thirty years ending 1870, 1871, 

 1872, &c. Then compare each sum with the ne.xt by the 

 dot method ; where each dot represents one value by the 

 horizontal scale, and the next by the vertical. .\ line may 

 be drawn connecting points of intersection of lines (hori- 

 zontal and vertical) from equal numbers in the two scales, 

 and two others roughly parallel with it (as shown). 



Now the last value, previous to this summer — the sum, 

 that is, of the thirty years ending 1908 — is 417. Find this 

 in the horizontal scale, and consider where the next dot is 

 likely to go. It would hardly be higher than (say) the 

 level of 433. Now we know the numbers of those days 

 in twenty-nine out of the thirty summers ending 1909 ; their 

 sum is 416. Deducting 416 from 433 leaves 17; and we 

 infer that this season would probably not have more than 

 seventeen of those hot days (which is only two more than 

 the average). The season has, so far, proved a very cool 

 one (.\ugust 4). This method is obviously capable of wide 

 application. 



If-ZO" IB '3(7 'uc 'SO '6&'yo 'so "■'^o Jtto 



-4va 



A similar conclusion seems to be arrived at by a com- 

 parison of Greenwich and Rothesay weather. It appears 

 (whatever the explanation) that when the year's rainfall 

 at Rothesay has exceeded 55 inches (last j'ear had 56), the 

 following summer at Greenwich has never been very 

 warm. \Ve may tabulate the cases (eleven in number, 

 1841-1907) as follows : — 



Rothesay Greemvlch day. Relation to 



Ri. with 80 or more , * 



in. following summer * ^ ^' 



A v. 10-4 

 That is, eight cool summers, three slightly warm, and the 

 hottest with seventeen of those days. It seemed not un- 

 reasonable to apply this " rule-of-thumb " (if it is to be 

 NO. 2081, VOL. 81] 



so called) to the present season, following on a Rothesay 

 year, which would fall to be added to the above list. 



Once more ; the summer season of 1S79 is well re- 

 membered as a singularly cold one. There were only 

 thirty days with 70° or more, and one with 80° or more 

 (the averages being 77 and 15 respectively) ; and now, at 

 thirty years' interval, we have another very cold sumrner. 



Suppose we compare each summer with the thirtieth 

 after, in respect of those very hot days (80^ or more). 

 We can carry the comparison obviously up to 1878 (that 

 year compared with 1908). 



It would appear that, in the case of very cold and very 

 warm summers, there is some tendency for the thirtieth 

 after to be of like sign in relation to the average. 



Thus the six coldest, in ascending order (o to 6 hot days), 

 are i85o, 1862, 1S41, 1853, 1855, 1S45 ; in each case but one 

 the thirtieth season after was cold, and that one was average. 



The six hottest, in descending order (40 to 27 hot days), 

 are 186S, 1S57, 1859, 1846, 1S76, 1870 ; in each case but 

 one (again average) the thirtieth season after was hot. 

 The season of 1909 seems likely to conform to this. 



Alex. B. MacDowall. 



P.S. (September 13). — ^There have been, so far, nine of 

 those very hot days (three in May, six in August), which 

 is probably the year's total, or near it. 



A New Mineral from a Gold-washing Locality in the 

 Ural Mountains. 



Some time ago I acquired through a friend two small 

 glass tubes, together containing about 5 grams of a bright 

 greyish-yellow crystalline powder. 



The manager of the gold workings in question noticed 

 several years ago in his troughs minute quantities of the 

 dust referred to, and commenced to collect it, but in spite 

 of the greatest care he was not able to find more than 

 about 10 grams during the subsequent years. 



The separation of the dust has been made easier through 

 the specific gravity of the microscopic crystals being =9. 

 Various analyses made proved the dust to consist of about 

 98-5 per cent, tantalum and about 15 per cent, niobium, 

 with 0001 per cent, manganese. We have therefore a 

 new mineral, namely, native tantalum. 



During the last six months no more traces of the mineral 

 have been found, notwithstanding the greatest possible 

 care taken to find more. It seems to have been here _ an 

 instance of an isol.ated formation, but it is not impossible 

 that the same mineral may be found elsewhere, associated 

 with gold and platinum, but is overlooked owing to the 

 small quantity and the fact that it has a lower specific 

 gravity than gold or platinum. 



Perhaps this information may be of interest to those 

 associated with gold or platinum workings, and may induce 

 them to look out for this new mineral, when it is not im- 

 probable there may be found other native metals as well. 



Newcastle-upon-Tyne. P. Walther. 



The Benham Top. 



In confirmation of Mr. F. Peake Sexton's contention 

 in Nature of September 2 (p. 275), that irradiation plays 

 no appreciable part in the necessity for thin Hnes on the 

 Benham top, I may add that the colours are equally well 

 seen when the top is viewed (i) through a narrow 

 diaphragm held close to the eye ; (2) through a magnifying 

 lens ; (3) in the monochromatic light of the sodium flame. 



Mv only objection to Mr. Sexton's theory was at first 

 the brilliancy of the colours in the light of the sodium 

 flame, but this difficulty at once disappeared when Mr. 

 Sexton pointed out that though blue objects cannot be 

 seen as such in that light (because there are no blue rays 

 present for them to reflect), it by no means follows that 

 the nerve centre for blue cannot be stimulated by the light 

 of a sodium flame. It will be seen, on reflection, that quite 

 different phenomena are involved in the two cases, and, 

 this understood, there seems to be no difficulty in accepting 

 Mr. Peake Sexton's theory, which is substantially similar 

 to that of Prof. Liveing, made at the time the top first 

 appeared, though Prof. Liveing did not seem to realise 

 that the case of the sodium flame presented no real 

 difficulty, and he suggested that the colours seen in that 

 light were due to the fact that it is not absolutely mono- 

 chromatic — a ouite unnecessary contention. 



Colchester, September 8. ' Charles E. Benham. 



