394 



NATURE 



[May 27, 1920 



century "differed much from that to-day," ^ but a 

 further cohsideration of Pepys's notes, taken in 

 conjunction with those of Evelyn, has led him to 

 modify his views, and he now thinks that, on the 

 whole, there is a good case for supposing that the 

 winters in the seventeenth century were more 

 severe than they are to-day. Sir John Moore, it 

 is true, maintained in a paper, " Is our Climate 

 Changing? " read before the British Association 

 (Section A) in 1908, that the British climate is not 

 changing ; his evidence is based mainly on ob- 

 servations during the nineteenth century, with 

 some from the eighteenth ; but the constancy of 

 the climate during the nineteenth century does 

 not seem to preclude a change having occurred 

 since the seventeenth, nor does it follow that a 

 change should be progressive. 



There muct, however, be a good deal more 

 evidence in scattered letters or diaries that will 

 in time throw more light on this important point. 

 In Swift's "Journal to Stella," which extends only 

 from 1710 to 1713, there are weather references 

 on seventy-eight days a year. The period is 

 short, but I think it bears out the contention that 

 winters with little frost or snow were exceptional. 

 On December 27, 1710, Swift writes: "Did you 

 ever see so open a winter in England? We have 

 not had two frosty days." This was probably a 



1 Qu.^t. Journ. Roy. Mft. Soc, vol. xlyi., p. 68. 



ja(^on de parler, for at least two frosts are men- 

 tioned previously, and one fall of snow. By a 

 frosty day it must be supposed that the diarists 

 meant more than a slight morning frost of one 

 or two degrees in the screen. If this is so, the 

 warmth of the early winter in 1710 was not very 

 exceptional, judged by present-day standards. 

 December 27, it must be remembered, corresponds 

 to January 8 new style, but in the last fifteen 

 years during which the writer has kept climat- 

 ological records there have been four, if not five, 

 winters when there has been no frost worth speak- 

 ing about until after the middle of January, in 

 Hanipshire at any rate, and these were probably 

 as "open " as the winter of 1710. 



Swift, on the whole, takes rather more interest 

 in the weather for its own sake than does Pepys. 

 He compares notes with " Stella " on the difference 

 between the weather in Ireland and in London, 

 but, of course, most of the references concern the 

 weather as it affected him personally. There are 

 many complaints of cold, wet, and heat, and Swift 

 seems to have had a constitution that was much 

 affected by hot weather. It is curious to find 

 that bad weather is frequently made an excuse 

 for dining with Mrs. Vanhomrigh at the time 

 when Swift was beginning that acquaintance with 

 her daughter " Vanessa " which was fraught with 

 so much tragedy. 



Optical Instruments in Industry. 



OPTICAL instruments, which proved their 

 worth in war, are now being more and more 

 utilised in developing the arts of peace. A short 

 account of some of the chief applications of these 

 instruments to industrial requirements, especially 

 the more recent uses, may therefore be not without 

 interest at the present time. 



Passing over the microscope with a brief 

 reminder of its modern use, in metallurgy, for 

 showing the structure of iron and other metals, 

 one of the first instruments to note is the refracto- 

 meter. In many chemical works this, in one form 

 or another, is invaluable as a means of controlling 

 the various operations, by reason of the sim- 

 plicity of its manipulation and the rapidity with 

 which the results are obtained. The refractive 

 index suffices in numerous instances to determine 

 the strength of chemical solutions. It is ascer- 

 tained in a few minutes, and only a drop or two 

 of liquid is required for the purpose if an instru- 

 ment of the Abbe type is employed. No weighings 

 are involved, and no calculations if the tempera- 

 ture is suitably controlled, so that liability to 

 error is greatly minimised. The instrument is thus 

 almost an ideal one for the control of works 

 operations where the degree of strength or purity 

 of a product is required to be ascertained by means 

 of rapid tests, or where a process has to be 

 stopped when the product has reached a certain 

 stage. Specific gravity determinations or simple 

 chemical titrations are often used in such cases, 

 NO. 2639, VOL. 105] 



but the refraction method is always quicker, is 

 generally more accurate, and sometimes possesses 

 other marked advantages. Thus the strength of 

 an aqueous solution of nicotine can readily be 

 obtained, correct within about 01 per cent., by 

 the refractometer, whereas the specific gravity 

 method is of no value in this instance, and titra- 

 tion results are vitiated if other basic substances, 

 such as ammonia, are present. 



Acetic acid, acetone, ammonia, ammonium 

 sulphate, carbolic acid, cream of tartar, glycerin, 

 and saltpetre mav be mentioned as products, made 

 on a large scale, for which the instrument is 

 useful. In the brewing industry the determina- 

 tion of alcohol, extract, and original gravity of 

 beer is readily made by means of the refracto- 

 meter. In the fats and oils industries, in the 

 fractionation of petroleum products, in the dis- 

 tillation of tar oils, and in the manufacture of 

 many pharmaceutical articles, the refractive index 

 is a valuable aid for controlling the purity of the 

 materials and finished products. It is useful also 

 in the manufacture of various viscous mixtures or 

 semi-solid pastes, in order to determine whether 

 the constituents have been adequately mixed, and 

 thus to obviate local excess or deficiency of the 

 active ingredients. 



The polarimeter is an instrument constantly in 

 use for the evaluation of essential oils, whilst 

 makers of starch products, tartaric acid, and 

 alkaloids frequently have recourse to it, and a 



