112 



NATURE 



|JUNE_I,.I^503 



' roaring forties ' of mariners." He further directs atten- 

 tion to the need of distinguishing between these two 

 weather systems, which play distinct parts in the meteor- 

 ology of this region. A study of the accompanying two 

 figures will indicate the importance of the islands of 

 Tristan d'Acunha and Gough (indicated by a black dot 

 towards the south-west), and also of Mauritius (the dot east 

 of Madagascar). The two former islands lie in the wind 

 system pertaining to the anticyclonic (high-pressure) area 

 on the west, the centre being indicated by the letter H, 

 while Mauritius, situated to the east of South Africa, is 

 in the south-east trade area in the system formed by the 

 high-pressure (anticyclonic) region, the centre of which is 

 marked also with an H. 



By observing the general trend of the air currents in- 

 dicated by the large arrow, it will be seen that for the 

 winter season in South Africa (Fig. i) meteorological 

 observations made in either Tristan d'Acunha or Gough 

 Islands would undoubtedly render valuable aid to the 

 weather forecasters. 



In the case of the summer months (Fig. 2) there is no 

 conveniently placed island that could furnish equal assist- 

 ance, but it seems very possible that use could be, and 

 most probably has been, made of the observations at 

 Mauritius for determining the strength of the south-east 

 trade current which impinges on the African coast at this 

 time of year. For forecasting purposes Mauritius, and 

 possibly Rodrigues, would have greater value for regions 

 further up the African coast. 



Unfortunately, the .'Vnisterdam and St. Paul islands 

 (marked with one dot) lie too far south and east to serve 

 as useful outlying stations for South Africa. On the other 

 hand, these islands should be undoubtedly utilised by the 

 .•\ustralians. 



An examination of the accompanying figures indicates 

 the relative positions of the Australian continent and this 

 large southern Indian Ocean wind system. These islands 

 will thus be seen to be right in the track of the current 

 which strikes the south and west coasts of Australia, and 

 should form ideal out-stations for gauging the general con- 

 dition of this wind system. 



That the prevailing winds on the west coast of Australia 

 come from a southerly direction is indicated in the follow- 

 ing table, which gives the number of times the wind has 

 blown from each point of the compass at the Perth Observ- 

 atory during the year 1002, the readings being taken eight 

 times a day : — 



N. 



N.N.W, 

 N.W. . 

 W.N.W. 

 W. 



W.S.W. 

 S.W. . 

 S.S.W. . 



s. 



S.S.E. . 

 S.E. . 

 E.S.E. . 

 E. 



E.N.E. 

 N.E. . 

 N.N.E. 



51 

 73 

 67 

 92 



H3 

 232 



432 

 425 

 24s 

 194 

 121 



IS7 

 139 

 '59 



Another table shows that the resultant direction of the 

 wind, at the same observatory for the same year, was 

 south for the months January to April and October to 

 December inclusive. 



There seems every reason, then, to hope that the utilisa- 

 tion of information from one of these islands for several 

 months in the year would in time amply repay the initial 

 cost and rnaintenance of the station. 



It is not without interest to remark that the air current 

 which passes the west coast of Australia in July (that is, 

 in winter in .Australia) becomes later the south-east trade 

 wind of the Indian Ocean, and eventually reaches the 

 Indian area in the form of the south-west nionsoon in the 

 summer months of the northern hemisphere. In the 

 months about July, Western .Australia is thus apparently 

 closely connected, meteorologically speaking, with India, 

 NO. 1857, VOL. 72] 



but in the months about January the connection is between 

 Australia and South .'Xfrica. 



The natural deduction to be made from the above is that 

 the meteorological services of all these countries should be 

 closely in touch with each other. Their combined efforts 

 will certainly considerably increase our knowledge of the 

 meteorology of this vast region, and each will benefit by 

 this mutual interchange of information. 



Although mention has only been made of one or two 

 instances in which the employment of islands as meteor- 

 ological stations would most probably be rewarded with 

 practical results, there are other countries that might 

 equally profit by adopting the same principle. 



It is, however, important for the study of world meteor- 

 ology that many islands should be employed as observing 

 stations. They may not be very ideal places for observers 

 to live in, but a change every few months, and the adop- 

 tion of self-recording instruments, would possibly simplify 

 matters. Where cables are lacking, and the island in 

 question is of great meteorological importance to some 

 continent, wireless telegraphy might be employed with 

 advantage. William J. S. Lockyer. 



An OPTICAL CONGRESS AND EXHIBITION. 

 "T^HE aims of the optical convention, which was opened at 

 ■*■ the Northampton Institute, Clerkenwdl, on Tuesday, 

 May 30, are to increase the interest taken in optical science 

 in this country, to promote an improvement in technical 

 education in optical matters, and to aid the development 

 of the British optical industry. In his address, the chief 

 part of which is subjoined, the' president. Dr. R. T. 

 Glazebrook, F.R.S., after explaining the origin of the 

 proposal to hold a convention, and the steps taken to 

 realise it, gives an outline of the history of optical progress 

 during the past two hundred and fifty years with the view 

 of illustrating the close union which has existed between 

 theory and practice at times of marked progress, and of 

 showing how each has reacted on the other in assisting 

 this progress. The programme of the convention includes 

 meetings for papers and discussions, which will be sub- 

 sequently published in a volume, and an exhibition of 

 optical and scientific instruments of British manufacture, 

 with a catalogue which is intended to serve as a work of 

 reference illustrating the productions of opticians in this 

 country. A description of some of the exhibits follows the 

 president's address abridged below ; and an article on the 

 nature and matter of the papers and discussions will appear 

 in these pages after the close of the convention. 



Progress of Optical Science and Manufactures.' 



The study of optics is a fascinating one, and its history 

 full- of interest. I do not propose to-night to attempt 

 to cover the whole ground, but to ask you to look at one 

 or two special periods during which, it seems to me, theory 

 and practice reacted on each other in a marked manner, 

 and to consider what lessons we may draw as to the 

 relation which should in these days of ours subsist between 

 the two. 



For this purpose I might go back to very early days. 

 Ptolemy in his attempt to discover the laws of refraction 

 — and wonderfully good the attempt was, as we know now 

 — Archimedes with his burning glass, if, indeed, he ever 

 made it, had both practical aims in view. But we will 

 start to-night nearer our own time. The end of the 

 seventeenth century is such a period. The telescope was 

 invented about 1608, the microscope at rather an earlier 

 date, about 1590, both, probably, in Holland. 



Galileo, hearing of this, made his first telescope in 1610. 

 In 1611 Kepler, in his " Dioptrica," described the astro- 

 nomical telescope with one or more convex lenses as the 

 eye-piece; with this exception, up to Descartes's book on 

 " Dioptrics " in 1637, no other form of telescope but 

 Galileo's was known. The law of refraction was first 

 enunciated by Snell in 1621. 



Thus by the year 1660 the importance of the telescope to 

 the astronomer was fully appreciated, and its limitations 

 were being realised. In 1663 Gregory published an account 



1 From the inaugural address delivered before the Optical Conv 

 May 30 by the president, Dr. R. T. Glazebrook, F.R.S. 



