March 17, 1887] 



NA TURE 



469 



he knows that every improvement initiated in Jena will 

 be watched by keen eyes in England ; and he has 

 evidence, which will be as welcome to him as his work is 

 to us, that we arc not likely to neglect any point of excel- 

 lence, provided only we can be made to see it as such. 

 I understand that Dr. Zeiss admits that the formulas on 

 which his apochroniatic objectives are constructed involve 

 far greater technical difficulties than were met with in 

 the older formula ; and this is evidenced by the great 

 number of separate lenses combined in the construction. 



Now it has long been my judgment, and a judgment 

 that has been confirmed by men of large practical expe- 

 rience, that errors of technical execution, when present, 

 are shown at once by deep eye-pieces ; with an object of 

 regular structure, whose image fills the field of the eye- 

 piece, the experienced eye readily detects a want of 

 sharpness. 1 am bound to say that the apochromatics 

 from Jena did not impress me by this test as having 

 accuracy of technical execution equal to the object- 

 glasses with which they were compared. 



On the other hand, I find that with the new apochro- 

 niatic made by Powell and Lealand 1 can employ 

 advantageously deeper eye-pieces than I had ever used 

 before. 



Now there is a less number of separate lenses in the 

 London objective, and whether this superiority is due to 

 the lesser number of lenses or to other causes I may not 

 determine. I refrain from details concerning the com- 

 parisons I, amongst others, made of the lower power 

 apochromatic of Zeiss, further than to remark that in my 

 judgment too much has been sacrificed to the object of 

 enabling the observer to employ very thick cover-glasses. 

 This is, no doubt, a convenience ; but if, as in Zeiss's 

 I /4-inch and 1,6-inch, the choice lies between object- 

 glasses that cannot be used for covered and uncovered 

 objects and object-glasses that, with a moderate range of 

 thickness for cover-glass, provide that facility, the latter 

 appear to me from a practical point of view to be the 

 better. 



I note with interest that Powell and Lealand have 

 made an achromatic oil-immersion condenser of N. A. r4, 

 and will probably be able to increase the aperture to I "5 

 in proportion as thinner glass is used to mount objects 

 upon. The mechanical part of this instrument had, when 

 it first reached me, a very neat form, but was difficult of 

 manipulation ; and this, involving as it did alteration, has 

 prevented me from really testing its merits. But I have 

 just received it, with a inechanical modification I sug- 

 gested well carried out, and I have little doubt but I shall 

 realise now its optical excellence. On the whole, then, 

 we may rejoice in the fact that a distinct advance has 

 been made in the optics of the microscope, and the 

 more so from a conviction that there lies considerable 

 potentiality still in the sources from which the amount of 

 progress made has resulted. 



ATLANflC WEATHER CHARTS 



''T'HE Meteoiological Council has just issued a folio of 

 A synchronous weather charts for the North Atlantic 

 Ocean and the adjacent continents, those now published 

 forming the first part of a series which embraces the 

 thirteen months from .August I, 1882, to .August 31, 1883. 

 The whole series is to be issued in four parts. Part i con- 

 taining the chaits from August I, 1882, to November 7, 

 1882. Two charts are given for each day — one shows the 

 barometer, wind, and weather, whilst the other gives the 

 air- and sea-temperature, and weather, the weather being 

 given on both charts for the purpose of easy comparison 

 with other elements. The isobars, or lines of equal baro- 

 metric pressure, are drawn for each tenth of an inch, and 

 figures are given in the central areas of the several de- 

 pressions to show the lowest reading of the barometer 



recorded by vessels passing through these disturbances. 

 The direction and force of wind are shown by a system of 

 arrows which fly with the wind, and the different forms 

 of arrows exhibit very readily where the wind reaches the 

 force of a gale, whilst the winds at high-level stations, 

 where the elevation is 4000 feet or upwards, are indicated 

 by red arrows. The air- and sea-temperatures are shown 

 by different coloured isotherms, or lines of equal tempera- 

 ture, which are drawn for each 5^ F. The weather, such 

 as rain, fog, or mist, is shown by different methods of 

 shading, and, as mentioned above, is given with each 

 style of chart. The synchronous hour for which the 

 observations are charted is noon Greenwich time, except 

 in the case of air- and sea-temperature, where local noon 

 has been taken in preference. No letterpress has been 

 published with the charts except a few explanatory notes, 

 in which it is stated that the study of the weather of 

 Western Europe for many years has established in a 

 manner that is beyond question that the atmospheric dis- 

 turbances, on which the changes of weather are in a 

 great measure, if not mainly, dependent, reach our 

 western coasts after having passed for a longer or shorter 

 distance over the Atlantic. The Meteorological Council 

 undertook the investigation with a view to ascertaining as 

 far as possible the conditions under which such disturb- 

 ances either originate in or traverse the Atlantic, and the 

 extent to which the direction of their course, their magni- 

 tude, and persistence, may be influenced by the general 

 meteorological conditions of the area within which they 

 are generated, or of the regions which surround that 

 area. 



The period embraced by the charts is that during 

 which the international system of circumpolar observa- 

 tions was being carried out, and data have thus been 

 obtained from very high northern latitudes, which could 

 not otherwise have been procurable, and by these means 

 the results embodied in the charts have not only been 

 rendered far more complete, but are of an exceptional 

 value, not likely to be soon equalled. Among the circum- 

 polar observations regLdarly used for the charts are those 

 made at Spitzbergen and Jan .Mayen, two stations which 

 add materially to the value of the information on the 

 eastern side of the .Atlantic, as they enable many very im- 

 portant barometric changes to be traced which would 

 otherwise be lost, and they help much in fixing the posi- 

 tion of disturbances which have skirted the British coasts, 

 and at the time when our weather is improving as these 

 bad-weather systems are passing away. 



There are, on an average, observations from rather 

 more than 400 ships for each day, in addition to which 

 there are daily observations from about 300 land stations. 

 In all 1 1,236 returns, each containing the records of many 

 days, have been received from about 3000 vessels. So 

 large a number of observations have never before been 

 used in the drawing of synchronous charts, and this of 

 itself renders the work quite unique in its character. The 

 area embraced, which extends from the Pacific Coast of 

 America to the east of Moscow, in the heart of Russia, 

 and from the Arctic to the Equator, enables the numerous 

 weather changes to be watched day by day for days 

 together, and allows of a very extensive and compre- 

 hensive view of the influence of the several varying 

 conditions of the weather. 



The charts show many very interesting features of 

 weather changes, and they exhibit very clearly the 

 general way in which the weather systems move from 

 west to east in the middle latitudes. They show very 

 frequent tracks of low-pressure areas to the north of the 

 parallel of 40', such areas being frequently observed over 

 the United .States ; and after traversing North America, 

 they intensify and develop energy on reaching the 

 .Atlantic, apparently gaining much of their strength from 

 the supply of vapour over the ocean. Many such storms 

 can be traced across the .Atlantic, while some die out 



