I 12 



NATURE 



[May 30, 1S95 



b worked out. It shows a principal maximum in April, a 

 secondar}' maximum in September, and chief minimum in 

 November. The intensity of solar radiation for equal altitudes 

 is greatest in winter and least in sunmier, a circumstance which 

 tends to equalise the winter and summer temperature. A great 

 diminution of tr.\nsmissibility is brought about by that pheno- 

 menon so characteristic of the middle- European continent, called 

 in Germany Hoheiiramh, an elevated stratum of peat-smoke 

 which gives a faint and rather pleasant odour, usually taken to 

 indicate the continuance of fine weather. The author finds 

 greater opacity in front of an atmospheric depression, and 

 greater transmissibilily after it. The clearest air is preceded by 

 a hea\-y summer rain. 



The Meteorological Council have published a valuable set of 

 monthly meteorological charts of the Red Sea, showing the 

 prevalent winds and currents, with other information of use to 

 seamen i>assing through the Suez Canal to India. The wind 

 observations alone number nearly 75,000, and have been supplied 

 from logs s|)ecially kept for the Meteorological Office, from ships 

 belonging to the Koyal Navy, and various other sources. Each 

 chart, of which (here are Iwenty-four, contains useful remarks 

 referring to the leading features, which are shown graphically, and 

 the introduction to the Atlas contains an interesting general 

 summary by Lieutenant C. W. Baillie, R.N., Marine Super- 

 intendent. The wind charts show that from October to 

 January northerly winds are prevalent over the northern half 

 of the sea, and southerly over the southern portion. From 

 February to May the northerly winds extend further south, while 

 southerly winds prevail from near Perim to about the l6th 

 parallel. From June to September, northerly winds blow over 

 nearly the whole sea. Gales are most frequent between 

 November and March ; they generally VjIow from the southward, 

 and are mostly met with in the southern part of the sea. The 

 currents are .somewhat erratic, and while occasional strong 

 streams are experienced locally, their velocity is not usually 

 great over large areas. The Gulf of Aden may be taken as an 

 exception, as the currents often set there with considerable 

 velocity. An interesting feature has been noticed in the range 

 of sea-temiwralurc in the Strait of Bab-el-Mandeb, near the 

 Island of I'erim, where it amounts to 26° at the [leriod of the 

 S.W. monsoon. The whole work shows evjrlencc of the great 

 care and labour bestowed uiwn it. 



The extent to which many of the AmeriL.in ngricultural 

 experiment stations are devoting attention to the culture of 

 small fruits and other minor crop:, is |)erhaps significant of an 

 impending change in the C"Conomic bearings of the management 

 of the soil, and of the |artial displacement of \\vi gt-andc ciilliire 

 which has hitherto almost monopolised the field of exiierimental 

 inquiry. liullctin No. 55 of the Purdue University Station, 

 Lafayette, Indiana, o)>ens with a description of experiments with 

 small fruits, carried out in response tn the numerous inquiries 

 received from farmers and others concerning the different 

 varieties of such fruit.s. Strawlierrics, raspberries, lilacklwrries, 

 currants, gooseberries, and grapes, form the subject of this 

 section of the rc|)ort. Field ex|>crinients with nuiize and oats 

 are next dealt with, and amnngst the results noted, it is stated 

 that Ijcttcr yields have followe<l the sowing of two bushels or 

 more of oats |>er acre than that of any smaller quantity. The 

 bulletin concludes with a notice of e\i>erimcnts with sugar beet ; 

 but in view of the des|x;rate condition to which the licet -growers 

 of France are at present reduced— <lespilc the artificial supjwrt 

 which the sugar industry there receives under the bounty 

 system— wc cannot .see any immediate hope for the American 

 l«et-»ugaf indu.4lry. This, indeed, is practically admitted in the 

 tnillctin, for it is said ; "The condition of the sugar business 

 throughout all »ugar-pro<lucing countries is such thai there seems 



NO. 1335, VOL. 52] 



to be little probability of capital being invested in beet-sugar 

 plants in this country at present." The [xiints which are reiwrted 

 upon include comparison of varieties, time of harvest, the re- 

 s])ective eftects of bacterial disease and l)eet scab on the sugar 

 content of beets, the efiect of loosening beets some time before 

 lifting them from the ground, special thinning, tests of foreign and 

 .■\nierican seed, and yiekl and cost of crop per acre. It is con- 

 cluded that, under more f.ivourable economic conditions, beet 

 factories might advantageously be established in the Slate of 

 Indiana. 



A PAPER by Wilhclm von Hezold, on the lines of equal 

 disturbance of the magnetic potential of the earth, appears 

 in a recent number of the Silz. der Akad. der Whs. zii Berlin. 

 The deviation of the jiotential at any place from the mean 

 value of the potential corresiKinding to the |)arallel of latitude 

 ixissing through this place being called the disturbance, 

 the author gives the theory of the lines of equal disturb- 

 ance. He shows that the westerly (or easterly) comixment 

 of the earth's magnetism is given by the rate of change of the 

 disturbance of the poleiuial along the parallel of latitude 



or VV = 





where \a is the disturbance for the potential, 



and by is an element of a latitude circle. Hence it foll.u^^ 

 that a knowledge of a westerly com|)onent of the earth's fall I 

 for the whole surface of the earth suffices to everywhere deiii 

 mine the disturbance in the magnetic potential, and draw,lhe lino 

 of equal disturbance. Wherever the lines of equal disturbann- 



are tangential to a circle of latitude- -" = o, and hence \V=o, 



dy 



or all such points will lie on the agonic lines, i.e. the lines along 

 which the declination is zero. M all places where the lines 

 of equal disturbance are t.angential to the terrestrial meridian 

 the northerly component of the earth's field has its normal 

 value. The author has constructed a chart of these lines for 

 the epoch 18S0, using the data given in the magnetic charts 

 published by G. von Quintus Icilius. The mean value of the 

 magnetic potential for the latitude \ is found to be given with 

 a high degree of accuracy by the expression V„ = K sin A, 

 and the author considers that this simple expression must have 

 some s|>ecial significance, anil not be merely an empirical 

 formula. 



A PAI'KK, by Mr. G. C. Whipple, eiililled "Some Observa- 

 tions on the Growth of Diatoms in Surface Waters" (Teclino- 

 logieal Quarterly, vol. vii.), is a valuable contribution to the 

 study of the periodic frequency of microscopic organisms in 

 freshw.ater areas. The work is noteworthy as having been carried 

 on in a biological laboratory attached to the Hoston WaUr Works. 

 The author's general results are here given : (1) That the growth 

 of diatoms in ponds is directly connected with the phenomena of 

 stagnation ; that their development does not occur when the 

 lower strata of w.ater are quiescent, on account of greater density, 

 but rather during those periods of the year «lien the water is in 

 circu'ation from lop lo bottom. (2) That diatoms flourish best in 

 ixjnds having muddy liolloms. { j) That in deep ponds there are 

 two well-detined |H."ri(Hls of growth -one in the spring and one 

 in the auUnnn ; thai in shallow ponds there is usually a spring 

 growth but no regular autumn growth, and thai other growths 

 may occur at irregular intervals as the wind happens to stir up 

 the water. {4) That the two most important conditions for the 

 growth of diatoms are a sufficient .supply of nilrales and a free 

 circulalion of air, and that both these omdilions are found at 

 those |)erif>ds of the year when the water is in circulation. (5) 

 That while lemi>eralure has po.ssil)ly a slight influence on the 

 growth of diatoms, it is of so little importance that it does not 

 affect their .seasonal distribution. (6) That the increiise of diatoms 

 takes place .subslanlially in accordance willi the law of geo- 



