May ]6, 1878] 



NATURE 



61 



It brings before that nerve such an accurate reproduc- 

 tion, so to speak, of the vibrations •which were communi- 

 cated to it at the other end by the vibrations of the 

 molecules of iron, that we have the impression that we 

 see a mass of white hot iron, because the ether was agitated 

 by precisely a mass of white hot iron in the first instance. 

 Now, if we observe any mass such as this, giving us light 

 in the ordinary way, we get merely the impression of form ; 

 but if we admit such white light to our eye through the 

 prism, we get it transformed into a band of colour 

 called a spectrum, because, as we have already seen, 

 white light is built up of a gamut of light notes from the 

 lowest note to the highest ; that is— to talk in the language 

 of colour — from the extreme red to the extreme violet, 

 through all those colours which are so gloriously brought 

 before us in the rainbow, and more too. 



But this does not happen with all substances. 

 Let us go now from our mass of white hot iron back to 

 those smallest particles of iron vapour, those ultimate 

 molecules to which I first drew attention. If we subject 

 the light which comes from them to the same treatment, 

 that is, if we allow it to come to our eye through a prism, 

 we find that we don't get the whole gamut of colour 

 represented as in the former case. We only get a light 

 note, so to speak, here and there. Ordinarily, the 

 phenomenon is presented to us in consequence of the 

 construction of the spectroscope, by a series of lines, 

 because ordinarily the spectroscope, is so arranged that 

 the vibrations from any set of molecules are made to 

 paint for us images of a fine aperture called a slit, through 

 which the light is made to pass. If the light is discon- 

 tinuous so far as the gamut of light is concerned, we 

 only get a light note here and there. If it is continuous, 

 the series of images is continuous; and we get what 

 is termed a continuous spectrum, that is, the band of 

 rainbow tints. 



Now, mark this well, that when we treat the vapours 

 of all metals that we know of in this way, we find that the 

 arrangement of these bright lines, the arrangement of the 

 images of the slit in other words, is different in the case 

 of the vapour of every metal, so that we may say that no 

 two vapours in Nature have the same colour. 



We are now justified in saying, speaking in the lan- 

 guage of molecules, that when we drive any chemical 

 substance down to its ultimate fineness, and cause the 

 ultimate molecules of each such chemical substance to 

 vibrate, the vibrations from each chemical substance 

 communicated to the ether and by the ether to our eye are 

 so distinct that if we will take the trouble to record the 

 effects thus obtained, we are for ever afterwards able to 

 recognise the vibrations of that particular molecule, in 

 whatever conditions we see those vibrations thus ren- 

 dered spectroscopically visible to us, whether the mole- 

 cules we are examining are in our laboratory, or in the 

 most distant body in the depths of space. 



The blue part of the spectrum which we obtain 

 when we examine the light which is communicated 

 to our eye by the vibrations of the finest particles 

 of manganese, to take an example, contains a series 

 of lines absolutely without any arrangement— a broad 

 band here, a single line there, a double line else- 

 where, and so on. In iron the arrangement of the lines 

 is perfectly different. They are more numerous, and 



a detailed examination would convince us that it is 

 quite as easy to make as definite a map of such a spec- 

 trum, and thus to point out the differences, as it is easy 

 to make a map or drawing of any two things which differ 

 in themselves. 



This is sure and certain knowledge. It seems to deal 

 with a condition of things with which the artist will never 

 have to do. This is so, but the necessity for the statement 

 of these facts will be abundantly seen in the sequel in which 

 I hope to show that between the two extreme molecular 

 stages to which I have drawn attention, that which always 

 gives us white light, and that which gives us coloured 

 light, the colour m no case being the same, we have 

 stages with coloured light which practically is always the 

 same for all bodies. J. Norman Lockyer 



THE AMERICAN STORM WARNINGS ^ 



O TORM movements from west to east over Europe are 

 ^^ familiar to your readers, yet I will refer briefly to them 

 here. The chief storm routes are as follows : — From the 

 regions immediately north of the British Islands to the 

 Norwegian coast and over the Scandinavian Mountains to 

 the Eastern Baltic and Central Russia, thence crossing the 

 Ural Mountains into Siberia. From the British Islands 

 directly to Denmark, North Germany, and Southern 

 Russia to the regions north of the Caspian Sea, and from 

 the British Channel, over the Netherlands, to Central 

 Europe, passing north of the Alps into the Danube 

 valley, and over the Black Sea to Asia Minor. The 

 influence of position of the area of high pressure south- 

 ward of the storm track on the direction of the latter is 

 very"great. Whenever the first described route is fol- 

 lowed, the pressure is high over Great Britain, France, 

 and Central Europe, and is falling in the Mediterranean 

 and Northern Africa. If the second route is taken by 

 the storm the barometer is high over Spain and the 

 Mediterranean, giving the zone of low pressure a gene- 

 rally eastern direction. When the last-described route is 

 followed, the pressure is high in the Atlantic off the coast 

 of France and Spain, leaving a relatively low pressure 

 over Great Britain, Southern Norway, and Sweden, the 

 Western Baltic, and_Central Europe. 



The heaviest rains occur along the west coast of 

 France and the British Islands, and on the Norway coast. 

 The precipitation lightens eastward and south-eastward 

 to Central Europe, but seems to increase again in the 

 Danube valley, where the influence of moist air from the 

 Mediterranean basin operates in increasing the energy of 

 the storm. Over the whole field minor disturbances are 

 frequently developed by the movements of the high 

 pressures, which rarely become serious storms. 



We must regard a knowledge of the general movement 

 of the atmosphere as essential to success in the prediction 

 of the movements of storms, their arrival in different 

 regions, and their character. During the past year I 

 have followed out and depended on the operation of what 

 I conceive to be a law of atmospheric movement which 

 I deduced from observations of the changes that occur 

 over the areas of the American and European continents 



' Cont'.nued from p. 34. 



