Feb. 12, 1874J 



NA TURE 



And to these sources of difficulty it might, we think, have 

 been added that, in consequence probably of our study of 

 geography from projections of the globe in which the 

 effect of perspective is designedly counteracted as much 

 as possible, we are apt to have a very defective idea of the 

 amount of apparent distortion which it occasions towards 

 the edges of the visible hemisphere. But even when all 

 this has been allowed for, wo find, the professor tells us 

 — nor indeed do we need opportunities as extensive as 

 his to convince ourselves of it — that the differences are 

 much too great to be altogether thus explained ; and he 

 concludes that the more conspicuous ones are errors in 

 representation. If there is occasional agreement as to 

 the forms, there is still nmch risk in referring them to the 

 same object, until it has been ascertained by computation 

 that the presentation of the globe towards the spectators 

 was nearly the same. Fortunately, during any given 

 opposition, the position of the planet's axis shifts but 

 liltie,andin otheroppositionsthe same presentation recurs 

 from time to time ; but instead of the correspondence 

 naturally anticipated, the differences are for the most 

 part, as he expresses it, " enormous." And yet amongtt 

 them all, coincidences come to the surface, too remark- 

 able to admit the idea of fortuitcus resemblance ; and we 

 must suppose that many who have taken pencil in hand 

 have not been sufficiently careful as to form and shading, 

 but have followed arbitrary and perhaps very mistaken 

 impressions, from which nothing but absurd and abso- 

 lutely contradictory inferences of a physical nature could 

 be drawn. T. W. Webb 



[To be conliniied.) 



THE ADMIRALTY CHARTS OF THE PACIFIC, 



ATLANTIC, AND INDIAN OCEANS* 

 ''T^HESE charts have been compiled by Captains Evans 

 -*■ and Hull, of the Hydrographic Departments of the 

 Admiralty, from Maury's pilot charts, Fitzroy's and Fer- 

 gusson's wind charts, charts issued by foieign Govern- 

 ments, and from the works of Dove, Ncumayer, Buchan, 

 and documents in the Hydrographic Office of the Ad- 

 miralty. They show for the (our seasons the pressure, 

 winds, and temperature over the parts of the globe covered 

 by the sea. January, February, and March are properly 

 grouped together into one season, these being the three 

 coldest months as regards the oceans in the northern, 

 and the three warmest in the southern hemisphere 



The most important piece of new work in these charts 

 is the " isobars,' or lines of equal barometrical pressure, 

 which are given for the seasons. These isobars for the 

 sea. taken in connection with Buchan's isobars published 

 in 1S68, may be regarded as the first approximation to a 

 complete representation of the earth's atmosphere over 

 both land and sea. We have minutely examined these 

 isobars, comparmg them with the large amount of new 

 information collected during the past five years from 

 many places situated on the coasts of the continents, or 

 in islands scattered over the ocean, and can come to only 

 one conclusion, viz., that the greatest care has been taken 

 in tlitir construction. Among the very few cases to 

 which slight exception might be taken is the isobar of 

 297 in. ot July, August, and September, drawn to south- 

 wards of japan, which observations do not appear to 

 warrant. It should also be pointed out that a serious 

 omission has been made in not stating how the ship baro- 

 metric observations were reduced to the mean pressures 

 from which the isobars have been drawn. 



We are now in a position to draw one or two general 

 conclusions of great importance regarding the distribution 

 ot atmospheric pressur^i over the ocean. In the ocean, 

 to westwards of each of the continents, there is at all 



* " Wind and Current Charts for tht Pacific, Atlantic, and Indian 

 Oceans," published at the Admiralty, October 1S72, under the superinten- 

 dence of Rear- Admiral G. H. Richards, C.B., F, R.S , Hydrographer. 



seasons an area, or patch, of high pressure, from o'lo inch 

 to 0'3o inch higher than is found on the coast westward 

 of which it lies. The distance of the centre of the space 

 of high pressure from tlie coast varies from 20' to 35° of 

 longitude, the average distance being nearly 30". The 

 position of the centre of the space varies from about 2;' 

 to 35- north or south latitude, or stating it roughly it lies 

 about the zones of the tropics. In these spaces the abso- 

 lute pressure is greatest during the winter months of the 

 respective hemispheres — a condition of things probably 

 due to the fact that during the winter season of the 

 northern hemisphere the great mass of the earth's atmo- 

 sphere is disposed about the tropic of Cancer, and during 

 the winter season of the southern hemisphere, about the 

 tropic of Capricorn. The position and shape of the iso- 

 bars seem to be largely determined by that of the conti- 

 nents adjoining. Thus the rounded form of the southern 

 portion of North America, the bending eastward of the 

 west coast of South America from Fayta to Arica, and 

 the form of the north-western part of Africa and its " lie " 

 from S.W. to N.E. are all more or less impressed on the 

 isobars bounding the contiguous spaces of high pressures. 

 These spaces are less prominently marked west of those 

 continents which have the least breadth in lat. 30' ; thus 

 the area of high pressure is less marked west of the Cape 

 than it is west of Australia, and still less than to the west 

 of North America. The isobars are much farther apart 

 on the western than on the eastern side of these areas of 

 high pressure ; indeed in many cases they are as it were 

 drawn out so as almost to reach the continent lying to 

 westward ; and in some cases there is even a tendency 

 towards, or the actual appearance of, secondary areas of 

 high pressure to eastwards of continental masses. This 

 is most distinctly seen to eastward of Australia. 



We have dwelt thus particularly on these spaces ot 

 high pressures because of their importance in atmo- 

 spheric physics, but more especially because of their vital 

 connection with prevailing winds and the genenal circula- 

 tion of the atmosphere. Out of these high pressures, the 

 wind blows in all directions anti-cyclomcally in accord- 

 ance with the well-known " Buys Ballot's Law of the 

 Winds," of which relation the wind charts before us 

 afford abundant confirmation. Keeping this relation 

 between wind and pressure in view, we have presented 

 in these high pressures the proximate causes of the 

 prevailing winds over the greater portion of the ocean ; 

 and through the prevailing winds, the drift currents and 

 other of the surface-currents of the sea ; and thereby the 

 anomalous distribution of the temperature of the sea as 

 seen in the Chile, Guinea, and other current?, and the 

 peculiar climates of the coasts past which these currents 

 flow. 



The small area of high pressure to the east of Australia 

 may be singled out as perhaps the most interesting of 

 the new facts in the charts. During win-er the winds 

 along the east and south of Australia blow inwards upon 

 the interior of that continent, whereas in New Zealand 

 the prevailing winds at the same season are north- 

 westerly and westerly, the directions being thus generally 

 opposite on these two co.ists facing each other. The 

 space of high pressure between gives a ready explanation 

 ot the direction of these winds, as well as of the heavier 

 rainfall on the west of the South Island of New Zealand 

 as compared with that of the North Island, and of the 

 south-east as compared with the south-west of Victoria. 



Like praise cannot be given to the charts of the 

 isothermals of air for January, April, July, and October. 

 In the October chart, the isothermal of 60" cuts the east 

 caast of South America near lat. 27° ; now at Monte 

 Video, the mean temperature of October is 61 '2°, at 

 Buenos A) res 61-3°, and at Bahia Blanca, in 3S°'4 S. lat. 

 5 9"" 7 ; that is, the isothermal of 60° should cut the South 

 American coast ii' ot latitude farther to the south. The 

 January isothermal of 60" is drawn passing through New 



