May 3, 1889.] 



SCIENCE. 



347 



LETTERS TO THE EDITOR. 

 Magnetic Storms and their Astronomical Effects. 



The earth is sometimes spoken of as a great magnet. Its mag- 

 netic condition, however, is not constant, but varies within rather 

 wide limits. Some of the changes are periodic, vfhils others are 

 spasmodic and irregular. The sunspot period appears to be in 

 some way related to the changes in the earth's magnetic condition ; 

 for, at the time when the spots are at their maximum in number, 

 the so-called magnetic storms are most frequent and violent. 

 There is a general agreement among meteorologists that the mag- 

 netic changes observed upon the earth are in some obscure man- 

 ner due to the influence of the sun. 



In meteorology, as elsewhere, when other explanations are un- 

 available, resource is found in electricity, especially so if electrical 

 phenomena can be in some manner discovered to be involved ; and 

 this happens to be the case in a very great number of phenomena, 

 not as causes, but as effects. Not infrequently it happens that 

 some of the best-known laws of electricity are ignored, or are con- 

 founded with other laws of other forms of energy. This seems to 

 be precisely the case in this phenomenon. 



In his article upon meteorology, in the last edition of the " En- 

 cyclopsedia Britannica," Balfour Stewart says, " We are thus driven 

 to look to the upper regions of the earth's atmosphere as the most 

 probable seat of the solar influence in producing diurnal magnetic 

 changes ; and it need hardly be said that the only conceivable 

 cause capable of operating in such regions must be an electric 

 •current. Now, we know from our study of the aurora that there 

 are currents in such regions, continuous near the pole, and occa- 

 sional in lower latitudes." And yet a little further on he argues 

 very properly that more knowledge seems to be needed before we 

 can assert that there are currents of electricity in regions where 

 conduction is impossible. 



Now, a current of electricity always implies conduction, and 

 conduction implies molecular contact. We are abundantly able 

 to prove this : for with such vacua as can readily be produced, say, 

 the millionth of an atmosphere, not only will electricity not traverse 

 it, but even Crookes's phenomena cease. At the height of a hun- 

 dred miles, the average free path of the molecules is measured by 

 feet ; and this renders it as certain as any thing we know in physics, 

 that electrical currents are impossible there, and hence, whatever 

 may be the explanation of the magnetic changes in the earth, they 

 are not due to currents of electricity in those high regions. 



Still the earth is a magnet. It has its poles, though these change 

 their position. The bulk of the earth with which we are acquainted 

 is made up of non-magnetic matter, having varying degrees of con- 

 ductivity ; the rocky part being very poor, while the oceans and 

 moist soils are conductors to such a degree as to permit commercial 

 use for telegraphic and other purposes, thus saving the cost of a 

 return conductor. The larger part of the surface of the earth is, 

 then, an electrical conductor. Whenever a conductor of electricity 

 is rotated in a magnetic field, an electrical current is the result ; 

 and such current is maintained so long as the rotation is continued, 

 the strength of the current depending upon several variables, the 

 strength of the magnetic field, the degree of conductivity, and the 

 rate of rotation. 



That electrical currents are continually traversing the crust of the 

 earth, has been established, since the telephone has provided us 

 with an instrument delicate enough for observation, and employed 

 by so many all over the earth. 



To be sure, it was known before that earth-currents were some- 

 times present, for upon occasions they were so strong as to inter- 

 fere with or stop telegraphic communication. Such interruptions 

 were generally coincident with auroral displays, but sometimes oc- 

 curred in the day-time, when auroral effects could not be seen if 

 they chanced to be present. As these earth-currents have been 

 found to be coincident with both magnetic disturbances and with 

 spasmodic solar action, — for several observers have noted solar 

 eruptions at times when the magnetometers gave evidence of mag- 

 netic changes in the field, and in one or two cases even determining 

 that the rate of transmission of the sun's action was the same as 

 that of light, — it follows that the earth acts as if it were rotating 

 in the magnetic field of the sun. 



If the sun be considered as a magnet, then its field extends to 

 an indefinite distance in space, and the earth must be rotating in 

 it ; and, so far as the earth is a conductor, there should be currents 

 in it : in fact, just what we discover. So far, the electricity is an 

 effect, and not a cause, magnetism being the preceding physical 

 state. 



A conductor moving in a magnetic field in such a manner as to 

 have electrical currents generated in it always suffers retardation of 

 its motion, as is illustrated by letting a coin fall between the poles 

 of a strong magnet, — a property utilized in modern galvanometers 

 to bring the needle quickly to rest. Such currents are technically 

 known as " Foucaull's currents," and the energy they represent is 

 at once transformed into heat in the conductor. The electricity is 

 but the transient state intermediate between the retarded motion 



and the rise in temperature. This series of physical relations viz. 



the rotation of a conductor in a magnetic field, the retardation of 

 the motion, the electrical current, and the final transformation into 

 heat of original energy of the mechanical motion — is a well-ascer- 

 tained series of effects, which is universal ; and thus it follows, that 

 so far as the earth has currents of electricity set up in it by the 

 sun's action, so far its rotary motion is retarded, and also its tem- 

 perature is increased, both effects not hitherto recognized so far as 

 I know. Of course, the retardation of motion is very small indeed 

 but it must be taking place, and in time will bring the earth to a 

 standstill. What the amount may be, there appears to be no way 

 of determining, because there is no way of ascertaining the strength 

 of the earth's currents, nor the earth's resistance, nor the strength 

 of the magnetic field of the sun. 



Furthermore, the retardation of other bodies in the solar system 

 may be traced to the same physical conditions instead of frictional 

 resistance of the ether, which has sometimes been hypothecated. 



Lastly, if the magnetic condition of the earth vanes, it follows 

 that the magnetic field of the earth varies, and all bodies in that 

 field are re-acted upon by it. The gases of the atmosphere at 

 high altitudes have free paths comparable with those in Crookes's 

 tubes, and might fairly be expected to exhibit similar phenomena 

 if electrified and in a changing magnetic field. Their electrifica- 

 tion need not be much of an assumption, when one considers what 

 happens in a thunder-shower. Rotating molecules, if conductors 

 of electricity, ought to have Foucault's currents in them when in a 

 magnetic field, and they should therefore be heated. As there is 

 no chance for conduction of the heat, the rate of vibration increases 

 till incandescence is reached. The only way in which the molecule 

 can unload its extra energy is by radiation. 



The motions seen in auroras may thus be due to the changes in 

 the magnetic field of the earth instead of to electrical currents cir- 

 culating in the high air. A. E. Dolbear. 



College Hill, Mass., April 23. 



Chrome Yellow considered as a Poison. 



The object of this note is to spread wide the facts that chrome 

 yellow is a poison, and that its use in food-stuffs is by no means 

 rare. 



The cases reported up to this time, in which toxic action is as- 

 signed to lead chromate and to chrome yellow, — bodies which 

 apparently all writers consider as identical, — are many more than 

 a hundred. Seemingly the first report is to be found in the Medi- 

 cal Times and Gazette of Dec. 24, 1S59, in which are set forth the 

 cases of six school-lads who were seriously poisoned by eating 

 Bath buns. These latter were shown to contain each " seven 

 grains of chromate of lead," which had been used as coloring- 

 matter in lieu of eggs. All of the six lads are stated to have re- 

 covered. 



In 1S74, Von Linstow was next to assign toxic action to these 

 bodies. He attributed to them the deaths of two children, within 

 his own practice, who had eaten possibly seven artificial bees which 

 had served to ornament a cake. Each of these bees had been col- 

 ored by about four nailligrams of "neutral lead chromate." The 

 cause of death was destruction of the coats of the oesophagus and 

 stomach, with puncturing of the intestines. The cases are reported 

 in Eulenberg's Vierteljah7-ssch>-ifi f. ger. Med., N.F. XX., and 



