276 



NATURE 



[May 5, 1910 



many of the families of moths and the subfamilies of 

 Noctuidae still to be monog^raphed are undoubtedly 

 much less numerous in species than those already 

 describsd. 



When we consider how very few species of insects 

 were known to entomologists a century, or half, or 

 even a quarter of a century afjo, the enormous in- 

 crease in our knowledge of this subject within the last 

 few Nears is simply marvellous, even to those who have 

 witnessed, and to some extent kept touch with, its 

 progress from day to day. 



Report on the Poultry Industry in Belgium. By 

 Edward Brown. Pp. viii+112. (London: National 

 Poultry Organization Society, Ltd., 1910.) Price 

 15. net. 

 J,N 1906 and 1907 Mr. Brown visited America, Denmark, 

 and Sweden to inquire into the methods followed in the 

 poultry industry, and during last year he visited Bel- 

 g'ium with a similar object. Probably in no country 

 in the world is intense production more general than in 

 Belgium, one consequence being that it supplies its 

 own poultry and egg requirements, and is not depen- 

 dent, like England, on imports from foreign countries ; 

 indeed, it has a surplus for export. 



Although in some respects the conditions in 

 Belgium resemble those obtaining in England, 

 there is the fundamental difference that the Belgian 

 farmer specialises in small animals, like poultry, 

 rabbits, even in pigeons and cage-birds as a 

 hobby, whilst the English farmer has gone in 

 for larger stock. Poultry-farming pure and simple 

 is not common. But everywhere Mr. Brown found 

 that poultry figured as an adjunct to the farm, 

 particularly on the small holdings. In some cases, 

 indeed, land did not come under cultivation until it 

 had been run over for some years by fowls, and 

 fertilised by their droppings. Thus the Campine 

 district, which extends from Malines east and north to 

 the Dutch frontier, was at one time merely a sandy 

 plain covered with fir trees. About thirty j'ears ago 

 the peasants began to raise chickens for sale to the 

 fatteners ; the industry spread, and now the trees are 

 g^one and the whole district is farmed. It would be 

 interesting to know how many tons of purchased food 

 were consumed per acre in effecting this change. Egg- 

 production is stated to be the main object, and the 

 birds are looked after by the women and children ; the 

 methods are, however, essentially simple, no more 

 elaborate appliance being- used than is absolutely 

 essential. 



The report contains a number of useful details, and 

 concludes with a number of recommendations. The 

 small holder in particular is urged to devote some, 

 though not all, of his attention to poultry, and it is 

 suggested that poultry-keeping should be encouraged 

 on land at present waste. Various methods of man- 

 agement are also recommended. 



Halley's Cotnet : its History, with that of other noted 

 Comets, and other Astronomical Phenomena, Super- 

 stitions, d^r. By Rev. John Brown. Pp. 52 ; illus- 

 trated. (London : Elliot Stock, 1910.) Price is. 

 net. 

 As a useful collection of facts and references concern- 

 ing- Halley's comet this small volume will take a 

 place in the mass of comet literature now appearing 

 so profusely. It contains nothing startlingly novel, 

 being, to a great extent, a compilation of interesting 

 oddments gathered, with due acknowledgments, from 

 various sources. In many places extraneous material 

 is introduced, rendering the book perhaps more in- 

 teresting, but less suitable as a precise account of 

 what itT presumes to deal with. The four illustrations 

 are rather crude and of no especial interest. 



NO. 2 1 14, VOL. 83] 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsible for opinionJKB 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejectei 

 manuscripts intended for this or any other part of Naturk. 

 No notice is taken of anonymous communications.] 



The Orientation of Crystals of Ice in a Flux of Hea*, 



It was found by Forbes man}' years ago that the therma 

 conductivity of ice was better along the principal axij 

 than at right angles to it. Straneo, in 1897, does no 

 come to any definite conclusion in deciding that such i! 

 the case. It is well known, however, that the formatioi 

 of surface ice by conduction always shows the principa 

 axis of the crystals to be normal to the freezing plane, orj 

 in other words, in the direction of the flux of heat fror 

 the underwater. Since ice is a better conductor of hea 

 than water, it is to be expected that if any difference exist! 

 in the conductivity in the two directions, the ice crysta 

 would form in such a way as to' dissipate the heat men 

 readily. 



During the process of the formation of an ice manth 

 in a rather large Bunsen ice calorimeter, my assistant, Mr 

 F. H. Day, directed my attention to a rather interesting 

 case, which, I think, proves the better conduction alonj 

 the axis of the crystal. The bulb of the calorimeter was 

 about two-thirds immersed in a freezing-point mixture 

 This particular calorimeter was unusually difficult to start; 

 and always refused to freeze when ether was rapidly 

 evaporated in it, or when a saline ice mixture was intro- 

 duced. In consequence, our custom has been to add some 

 liquid air or solid carbon dioxide, as most convenient at 

 the time. In this case we used solid carbon dioxide. The 

 undercooling must have been considerable around the inne 

 glass tube, and a sharp temperature gradient result© 

 between the lower part of the glass and the walls of th 

 calorimeter. Heat was flowing in from the freezing-poir 

 mixture, but near the surface the heat flov/ed in mor 

 rapidly around the exposed portion of the bulb. The ic 

 formed as usual, but on withdrawing the calorimeter fo 

 inspection we found, growing out from the solid mantl 

 of ice, long needles and thin plates, which were perfect!; 

 orientated along the lines of the flow of heat. The crystal 

 near the top of the mantle were directed at an angle up 

 wards, while those at the base were found normal to th< 

 mantle surface. Between these positions the crvstals i?rew 

 at a corresponding inclination to the mantle surface. This 

 I think, conclusively shows the path of best conductivity it 

 the ice crystal to be along the principal axis. 



H. T. Barnes. 



McGill University, April 19. 



Zeeman Effect of the Yellow Mercury Line X 5770. 



It is well known that the separation of the mercurj 

 line \ 5770 in a magnetic field into a triplet is abnorrnal 

 inasmuch as the value of the ratio e/m of vibrating 

 electrons is much greater than that obtained from experi- 

 ments on kathode rays or from measurements of th 

 Zeeman effect on other lines of mercury and of other 

 elements. Lohmann first noticed that the line is separatee 

 into a nonet in strong fields, but did not investigate its 

 type. By using an echelon spectroscope of resolving powei 

 430,000 for A — o-5/i, I found that the distribution of lines 

 in the nonet can be accurately examined by using 

 vacuum tube of special construction. From a field oi 

 18,000 gauss upward, the lines composing the nonet war 

 distinctly observed with my instrument. They are diS' 

 tributed in three groups of three lines each, closelj 

 arranged at equal intervals, and each group occupies th« 

 position of the normal triplet. No dissymmetry wit! 

 respect to the middle line was noticed. Several measure- 

 ments in fields between 18,000 and 28,000 showed that th< 

 separation of lines in each group is proportional to th< 

 field strength, so that in weak fields each group appear! 

 as a single line. The lines of the middle group are equall] 

 bright, but the intensity of the remaining two groups 01 

 lines diminishes as we proceed outwards, just as is th« 

 case with the mercury line 5461, which is also divided intt 



