75 



NATURE 



\Nov. 23, 1876 



of v/hich document will always be a disputed point with 

 entomologists, inasmuch as (although twice quoted by 

 its author in his subsequent works) it is more than doubtful 

 whether it ever was actually published. 



The succeeding chapters are devoted to the differential 

 characters of the family, to structural details, habits, 

 development, secondary sexual characters, origin of the 

 genera and species, and mimicry ; then follow concise 

 descriptions of the genera and species, with comparative 

 and other valuable notes, descriptions of preparatory 

 stages, &c. 



It is a subject for congratulation, the importance of 

 which none but the working lepidopterist can fully appre- 

 ciate, that Dr. Packard has devoted six of the plates to 

 the delineation of wing structure ; most of the generic 

 errors in Mr, Walker's lists must be attributed' to his 

 entire neglect of the characters offered by neuration ; 

 attention to this is sometimes the only means by which 

 species, otherwise wholly similar, can be distinguished. 

 The structure of the thorax, although of much importance, 

 can rarely be attended to, as the destruction of the speci- 

 mens is necessary before it can be detected ; but in the 

 examination of the wing-veins nothing is needed but a 

 bottle of benzine, a brush, and a pocket lens, to reveal all 

 that is required without injury to the insect. 



In conclusion we heartily congratulate Dr. Packard on 

 having produced a work in every respect worthy of him- 

 self and the Academy of which he is an officer. 



A. G. B. 



LETTERS TO THE EDITOR 



[The Editor does not Jiold Jmtiself responsibte for opinions expressed 

 by his correspondents. Neither can he unda'take to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications ^^ 



Prof. Balfour Stewart on Meteorological Research 



It occurs to me to make the following remarks with reference 

 to Prof. Balfour Stewart's proposal in Nature, vol. xiv. p. 388. 



I cannot see any objection either to the nomination of the 

 council which is suggested, or to its constitution, provided each 

 existing society is duly represented by a member who can, when 

 circumstances seem to require it, attend and vote at any meeting 

 of the Council in London. I quite agree with the Professor in 

 thinking that the time has now come when our country should 

 resolutely grapple with the data which have accumulated in past 

 years and with those that are now being obtained. It is only by 

 a thorough discussion of meteorological data that the importance 

 of certain principles can be detected, and the necessity for altering 

 the modes of observing can be demonstrated. 



I do not see that the appoiniment ot the proposed council 

 should interfere prejudicially with the working of the different 

 societies. While it is the duty of such societies to procure the 

 facts, it seems to me essential in order to secure uniformity in 

 instrumental observation, without which all deductions or genera- 

 lisations from the data may be w^ rse than useless, that a council of 

 control should be appo nted in order to lay down rules forregulating 

 all observers. I would not give an arbitrary power to that council 

 to compel every society to adopt their views, because I have a 

 great aversion to centralisation in matters of science, for in some 

 cases the branches may be more in the right than the head ; but 

 in the event of a society declining to comply with the rules 

 issued by the council, that society should not receive Government 

 aid excepting for work that is done in terms of the rules. I take 

 it for granted, however, that the council would give due weight 

 to the arguments which were adduced )rom time to time by the 

 representatives of the different societies. I am further of opinion 

 that the different bodies should not only be allowed but encou- 

 raged by Government aid to prosecute independently in their own 

 way, any special subject which they may choose to take up. 



I hold so very strongly the absolute necessity of uniformity in 

 instruniental observation, ihat I should be disposed to recommend 

 each society to adopt almost any change in the forms of instru- 

 ments, in the kind of exposure, in the hours of observation, in 

 the form of protecting boxes, or in any other matter which might 

 be recommended by the proposed council, provided such 



changes were practicable, and were agreed to once for all by the 

 other societies in this country, and by foreign nations. 



I think it right to add that I am only stating my own indivi- 

 dual convictions, and do not in any way profess to represent the 

 opinions of the Council of the Society of which I am the hono- 

 rary secretary, although I have no reason to suppose that they 

 would take a different view. THOMAS Stevenson 



Edinburgh, November i8 



Ocean Currents 



In the report published in Nature (vol. xiv., p. 492) of an 

 address given at the Glasgow meeting of the British Associ ition, 

 September 11, by Sir C. Wyville Thomson, and revised by the 

 author, the following passage occurs : — 



"We have come to the conclusion that this great mass of 

 water is moving from the Southern Sea, and there seems to me 

 to be very little doubt — although this matter will be required to 

 be gone into carefully — that the reason why this water is moving 

 from the Southern Sea in a body in this way, is that there is a 

 greater amount of evaporation in the North Atlantic and over 

 the northern hemisphere generally, than there is of precipitation, 

 whereas it seems almost obvious that in the southern hemisphere 

 in the huge band of barometric low pressure round the south 

 pole, the precipitation is in excess of the evaporation." 



Now I quite feel that I am guilty of very great presumption 

 in challenging in any way the theories of so great an authority 

 as Sir C. W. Thomson, and my only excuse for the remarks I 

 am about to make is that there are some points that I and many 

 other seamen would like to have cleared up before we entertain 

 such an hypothesis. 



1. Have the investigations of the Challenger sufficiently proved 

 that there is no compensating or return current from the North 

 Atlantic to the South Atlantic Ocean? Especially, is it quite 

 certain that a stream of water from the Arctic regions does not 

 set southerly along the West Coast of Africa, i.e., south of the 

 equator ? 



2. Allowing that the precipitation in the Antarctic regions is 

 greatly in excess of that in the Arctic regions, is the precipita- 

 tion in the north torrid and north temperate zones less than the 

 precipitation in the south torrid and south temperate zones ? 



3. Looking to the much larger distribution of land in the 

 northern hemisphere, is it likely that the evapoiation there is in 

 excess of the evaporation in the southern hemisphere ? 



4. P^ven supposing the evaporation in the northern hemi- 

 sphere to be in excess of that in the southern hemisphere, can 

 it be shown that this vapour is carried to the Antarctic regions 

 for condensation, or can the excess of precipitation in the Ant- 

 arctic regions be accounted for in a more probable manner ? 



In answer to the first question I can only say that I am not 

 able to gather from the reports of the ocean soundings and tem- 

 peratures ot H.M.S. Challenger, published by the Admiralty,^ 

 that it has been at all proved that there is no compensating 

 stream of Arctic or other water. 



In answer to the second question, I have never heard it dis- 

 puted, and my experience as a seaman leads me to doubt the 

 possibility of reasonably disputing, that the rainfall in the north 

 temperate and north torrid zones is not only not less, but that it 

 is far in excess of the rainfall in the south torrid and south tem- 

 perate zones. Maury (and no matter to what extent we may 

 differ from his theories, we must give due weight to his data) 

 says that the total amount of rain in the north temperate zone is 

 half as much ajjain as in the south temperate zone. 



With reference to the third question, whether the evaporatioE 

 in the northern hemisphere is in excess of that in the southerij 

 hemisphere, I think the onus of proof rests with those whd 

 start the theory, but in my present state of ignorance on tha 

 subject I must confess that it is to my mind quiie inconceivable 

 There are, with few exceptions, no large rivers in the souther 

 hemisthere, and surely the discharge into the sea of the larg^ 

 rivers in the northern hemisphere must be regarded as the return 

 to the ocean of the excess ot precipitation over evaporation in the 

 regions which they drain. 



There remains the fourth question, and before trying to answer 

 this I should like briefly to state what I think is the general of; 

 accepted belief up to the present time with reference to atmo-^ 

 spheric currents or circulation. The trade winds are supposedj 

 to be currents from the poles which, starting from the PoL 



I Plate VI. Report No. 7 would appear to indicate that Arctic water doesj 

 cross the equator. 



