May 1 6, 1878] 



NATURE 



63 



portion of the Atlantic and Gulf States maybe considered 

 as permanently within the wave-lines of the zone of high 

 pressure. This means that the curving of the northern 

 and the southern margins of the zone give to these 

 regions their prevailing winds, which, in the case of 

 Florida and Georgia are called the 'trade-winds.' In 

 the mid-Atlantic, north of the latitude of thirty de- 

 grees, there is another permanent area of high pressure 

 and on the southerly side of the area are experienced the 

 "trade winds.' Now what are these 'trade winds' 

 after all, but the westward flow of the air along the undu- 

 lating southern margin of the zone of high pressure. 



" Sometimes the zone of high pressure becomes com- 

 pressed to a narrow band between two areas of low 

 pressure, and large areas of high pressure will be formed 

 both east and west of the narrow part of the zone. . . . 



" You will naturally desire to know how we reconcile 

 the development and movements of tropical cyclones 

 with the foregoing statements. Although the subject is 

 one that demands a more special treatment than it can 

 receive from me now, I will state that, when at the period 

 of the equinox the solar influence becomes a disturbing 

 element in the meteorology of the equatorial zone, the 

 alignment of the axis of the zone of high pressure 

 becomes a compound curve, so as to present to the 

 westerly flow of the winds and the ocean current a mar- 

 gin of the zone, in the hollow of whose undulations a 

 vortex'is developed. This, by cumulative energy, travels 

 around the wave curve presented to it, and then moves 

 away along the southern margin of the zone of high 

 pressure toward the European coast. The cyclone that 

 devastated Indianola and Galveston in September, 1875, 

 passed almost in a straight line from South Carolina to 

 Valentia, Ireland, and thence probably over Southern 

 Sweden into Northern Russia." 



To these remarks I would add that the zones of high 

 pressure sometimes come together but do not merge, and 

 that disturbances moving along the partly-closed zone of 

 low pressure toward the region of contact between the 

 two high-pressure zones, have the necessary energy to 

 divide them again, and thus open a passage eastward 

 between them. On the other hand, the zones close on a 

 depression, and lift it to the higher levels of the atmo- 

 sphere, where its humidity is condensed into rain that 

 falls over a region whereon the surface-pressures are 

 high. 



With the object of utilising the zone law for the pur- 

 pose of predicting the movement of storms across the 

 oceans and continents, the meteorologist must watch 

 the axial and marginal undulations, and be always aware 

 of the general direction of the former. If this know- 

 ledge is possessed the prediction of storm movements 

 becomes a simple matter of close observation and experi- 

 ence. To those who devote their whole attention to the 

 work no difficulties can arise, because nature has fixed 

 within certain degrees the limits of deviation which storm 

 movements assume outside the normal courses for each 

 class. The attendant conditions, such as rains, winds, 

 variations of temperature, and humidity, and the presence 

 of superabundant electricity are subject to greater or 

 lesser modifications according as the storms traverse 

 regions of land, water, mountain, or plain. I would call 

 special attention to the appearance of storm centres over 

 Norway and Eastern Russia, of which no serious indica- 

 tions of their movements were observable in the British 

 Islands and France. Such storms occur always when 

 the pressure is high over the countries last named, and 



they pass along the northern margin of the zone of high 

 pressure north of the Hebrides or between the Faroe 

 Islands and Iceland, and then move in a south-easterly 

 direction with the undulation into the Baltic and the 

 great plains of Russia, where they sometimes develop 

 considerable energy. This is due to the operation on the 

 eastern slopes of the Scandinavian Mountains of the 

 same causes that combine to produce the north-western 

 storms of Montana Territory. 



It is unnecessary to refer to the local phenomena of 

 European storms ; they are so fully understood that it is 

 impossible to add anything to the acquired information 

 regarding them. Yet I mention them in the hope that 

 some of the suggestions I have offered in the foregoing 

 may be applied to the study of their development and 

 nature. Jerome J. Collins 



SOLAR RADIATION 

 Les Radiations chimiques du Soleil. Par M. R. Radau. 

 (Paris : Gauthier-Villars, Imprimeur-Libraire, Quai des 

 Augustins, 1877.) 



THE importance of an accurate registration of the 

 comparative intensities of solar radiation is not to 

 be over-estimated at a time when so much diversity of 

 opinion exists regarding the climatic effect which the sun 

 produces upon our earth. Such radiations have been 

 divided into three classes, the heating, the visible, and the 

 chemical or actinic ; and though the whole of these three 

 divisions are for the most part arbitrarily defined, yet 

 such a mode of denoting the rays of light lying between 

 certain limits in the spectrum is on the whole convenient, 

 if the proper mental reservation be made. In the work 

 before us we have an account of the various researches 

 that have been made by different physicists for obtaining 

 a measurement of the comparative intensities of the 

 chemical radiations. An absolute measure of their energy 

 has, up to the present time, been found impracticable, 

 but by noting the amount of change produced by them 

 in what are known as sensitive compounds, a comparison 

 of the otherwise immeasurably small quantity of work 

 that they are capable of performing can be made. The 

 amount of chemical decomposition or combination, caused 

 by the work performed by these rays, is in reality a 

 measure of the work performed by some previous che- 

 mical operation together with the infinitely smaller 

 quantity, due to the energy in these radiations. All 

 processes, therefore, which have been employed for the 

 purposes of actinometry, give results which are com- 

 parative measures of intensity, and not of absolute energy. 

 Perhaps the nearest approach to an attempt at a measure- 

 ment of the latter was by means of the chlorine and 

 hydrogen actinometer of Bunsen and Roscoe, certain 

 absorption experiments with which have been well described 

 in the work before us. 



In the introductory matter are cited the comparatively 

 recent researches of Vogel of the Berlin Industrial College, 

 in which he shows that by the addition of certain dyes to 

 silver bromide he is able to alter the position of maximum 

 sensibility of this compound to the spectrum. The results 

 of these experiments are certain, but the explanation 

 offered is perhaps more doubtful. It may be remarked. 



