July, 1903. 



KNOWLEDGE. 



155 



But may we conclude that it will be the same in all the 

 other regions of the Milky Way ? Here again, though we 

 must not positively affirm anything, I am inclined to 

 believe that more complete investigations will not Inad to 

 very materially different results. Still we already know 

 that the distribution of different stellar classes, in this 

 connection, is not the same for different regions of the 

 zone. Thus, when we treat of the " relative frequency " 

 of stars of different magnitvides as we have done above for 

 near y Cygui, we can say that the mean brilliancy of stars in 

 the Milky Way approximates much more nearly to the 

 bright classes in the northern regions near Cepheus, 

 whilst this mean magnitude is much feebler towards the 

 south in the regions of Aquila and Scutum. I have tried to 

 explain in former numbers of this magazine (Knowledge, 

 1902, July and August) for what regions these peculiarities 

 of distribution appear to me of the greatest interest for 

 leading us to conclusions as to the probable distance of 

 parts of the Milky Way. 



Uotterdam. 



THE SURROUNDINGS OF THE "AMERICA" 

 NEBULA. 



By Dr. Max Wolf, f.r.a.s. 

 Photographs of this fine nebula have been published 

 not only by myself (Knowledge, 1902) but also within 

 the last few months by Dr. Roberts and by Professor 

 Barnard. On these occasions, however, only the nearest 

 surroundings have been reproduced. Owiug to the great 

 interest of this beautiful object I have prepared a repro- 

 duction of a whole plate, showing the situation of the 

 nebula in the thick cloud of the Milky Way, which is so 

 striking to the naked eye as we look eastward from Deneb. 

 On this reproduction we see much better the faint nebulous 

 matter filling the dark channels between the stars to the 

 east and west of the "America" Nebula. The great 

 differeijce in appearance between the crowds of stars and 

 the nebulous parts is very well seen. The most interesting 

 parts seem to be the streams and clouds at the western 

 side of " America " between the bright stars. The repro- 

 duction is of the same size as the original plate, and is 

 made by contact printing only, and without any retouching. 

 Scale: — One degree = thirtv-five millimetres. 

 Koiiigsfidil, Heichlhenj, February, 1903. 

 -♦- 



[Tbe Editors do not liold themselves responsible for the opinions 

 or statements of correspondents.] 



RAKE CONDITION OP THE HUMAN HAIR. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — If one examines closely the variations of the 

 hair on many human subjects, interesting facts frequently 

 appear. One of these I found lately on the bauds of a 

 man aged 23, whose skin was generally very hairy. The 

 dorsal surfaces of his hands and fingers presented, in the 

 \isual jtlaces where hairs are found, groups of black points, 

 and among these a very few stmy liairs of ordinary length. 

 On the dorsum of the hand the black points were only 

 seen at the radial and ulnar bonk>rs, the surface between 

 being clothed with iiair of the nsual kind. When one's 

 finger was passed over these black points, against the 

 proper slope of hair of the part, the skin felt quite smooth. 

 Examination with a lens showed that the black jioiuts 

 were shafts of hairs which did not project above the 

 epidermis. The appearance was indeed more like that of 

 the black dots so coninion on other parts of the sliin, and 

 due to acne, than like the ordinary worn-down appearance 



of hairs, and the man said that as far as his recollection 

 went Vjack he had noticed the black points to be just as 

 they are now. I may add that no similar state of the 

 skin and hairs was to be found on the feet. This condi- 

 tion of the human hair is very rare, and I have never met 

 with it before. As far as it goes it supports the view that 

 the worn-down bristly state of the hair on the digits, so 

 often found in man, is due to a mechanical cause, viz , 

 constant friction of the hair against external objects, and 

 not to any true degeneration of man's hairy covering of 

 which this is a small part. The phenomenon noted here, 

 dating as it does from a very early period of life, tends to 

 show that the worn-down state of the hair was inherited. 



Walter Kidd. 



SOLAR ACTIVITY AND TERRESTRIAL 

 MAGNETISM. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — In a recent contribution to the Astrophygical 

 Journal (November, 1902), the writer of the same, Mr. 

 A. L Cortie, throws doubt on the observations made by 

 Prof. Young at Sherman in 1872, and contends that the 

 phenomena observed by Prof. Young do not stand in the 

 relation of cause and effect, as regards some sharp twitches 

 of the magnetic needle, apparently synchronous with 

 several directly observed spectroscopic disturbancjs. I 

 have always attached great importance to these particular 

 observations of Prof. Young, who, needless for me to 

 say, is a most conscientious and careful observer. His 

 observations not only deal with a solar disturljauce and not 

 with a spot as such, but they incidentally favour the idea of 

 a 8pH-located cause. Mr. Cortie, as I understand, takes uj) 

 the position that spot-areas cannot be directly expressed in 

 values of magnetic force. Prom this view I think hardly 

 anyone will be prepared to differ, but that opinion does 

 not necessarily include the displacement from the sun of 

 the cause of the terrestrial magnetic disturbance. At any 

 rate, many observational reasons point the other way. 

 These I gave your readers in a letter on this subject in the 

 December issue of Knowlkdge. 



On looking the matter up again in Young's " The Sun." 

 I come to the conclusion that to label Young's observations 

 and deductions " coincidences " is, in my humble opinion, 

 unjustified. At the same time it must be stated that 

 Young himself leaves the matter pretty much an open 

 question. Mr. Cortie tells me that if I did study the 

 curves for the days in question I should modify my 

 opinion. I went to" examine the Greenwich observations, 

 but was unable to find a record of the curves, and must. 

 therefore, rely on the di.igram given in " The Sun " as a 

 faithful re]n-esentation of the magnetic records of the two 

 days. And there are, on August 3rd. 1872, three distinct 

 solar paroxysms taking ]>lace at clearly defined time- 

 intervals, each strictly simultaneous with the mechanically 

 recorded magnetic disturbances. The diagrams do not 

 evince suflicient general excitement to screen in the least 

 the three distinct jerks of the needle. Contrary to Mr. 

 Cortie's opinion, I consider, therefore, the case just cited 

 as much more convincing than the one which took place 

 two days later, in the proportion of three events ag.iinst 

 one. Mr. Cortie misses the point when he says of the 

 second case that it was nothing unusual, because it 

 occurred at the tag end of a magnetic storm. . The point 

 is that particularly strong outbursts on the sun were 

 directly observed at a definite time and the magnetic 

 recording instrument resptmded at that pi-ecise moment by 

 distinct and] ironouncedly sharp excursions. For this reason 

 then is the case of August 3 stronger, inasmuch as this sya- 

 chn-iiisni r.'iiciiled itself three times within 3^ hours. 



