April 1, 1893.] 



KNOWLEDGE 



73 



Dr. Eobert Mimro, in the Fortnifihthj Review, in an 

 article on " Preliistoric Trepanning," says : " The first 

 person to call attention to the fact that trepanning had 

 been practised in prehistoric ages was Dr. Prunieres, of 

 the town of Marvejol, who found a perforated skull in his 

 researches among the dolmens in his neighbourhood, some 

 twenty years ago. Dr. Paul Broca subsequently devoted 

 much time and study to the subject, and added greatly to 

 the facts already known by his researches in the artificial 

 caves newly brought to light in the Valley of Petit Morin. 

 He discovered that the polished portions round the margin 

 of some of the perforations were due to cicatricial deposits, 

 and concluded that during the neolithic period a surgical 

 operation was practised, which consisted in making an 

 opening through the skull for the treatment of certain 

 internal maladies." 



There seem to be serious prospects of a failure of our 

 india-rubber supply, and consequently the price of gutta- 

 percha has considerably increased. Last year it was 

 4s. 6d. per pound. Efforts are now being made in the 

 Indies, especially in the neighbourhood of Saigon, to 

 create large plantations, but it will take many years before 

 these young plantations can yield. In the meantime it is 

 suggested that a more rational method of extracting the 

 gum or gutta-percha should be adopted, so that existing 

 trees may not be altogether destroyed. Some day, pro- 

 bably, Africa will send us a good deal of this most valuable 

 substance, new applications of which are continually 

 arising. Prof. Tilden, F.K.S., of Birmingham, has recently 

 succeeded in making a chemical compound with somewhat 

 similar properties. If chemists can make a substance 

 equally good, they will confer a great benefit on the 

 community. 



Hctttrs. 



[The Editor does not hold himself responsible for the opinions or 

 statements of correspondents.] 



*-*M 



To the Editor of Knowledge. 

 Sir, — I see that I have made it appear in my last article 

 as though the crinoid originally described as Pcntacrinus 

 europceus really belonged to that genus ; whereas, of course, 

 it is the larva of the common feather-star [Antedun, or 

 Comatulii). I had intended to refer to it merely as the 

 first-discovered living crinoid in a general, and not in a 

 generic sense. R. Lydekker. 



THE IGNIS FATUUS. 

 To the Editor of Knowledge, 

 Dear Sir, — In his interesting article " On Certain Low- 

 lying Meteors," in your March number, Mr. Tomlinson 

 asserts that " the innis/dtiius is now seldom or never seen." 

 Perhaps I may be permitted to instance a very fine example 

 of it in this neighbourhood. Three miles north of here 

 there is a small deep dam, which serves as a reservoir to 

 supply the railway company with water for their 

 locomotives, and on which I, with a few friends, have 

 skated, whenever it has been sufficiently strongly covered 

 with ice, for many winters past. It has been our custom 

 to take a borer with us and make a small hole in the 

 centre of the ice, through which a stream of CH, issues, 

 and which we ignite by applying a lighted match, when a 

 pale blue flame, rising occasionally to a height of three feet, 

 appears ; in bright sunshine this becomes practically 

 invisible, but it is undeniably very hot. The feeding stream 

 runs through fields and along hedges, bearing vegetation 

 derived from these into the pond. 



Would not Major Blesson's ir/nes fatui in the Gubitz 

 forest consist rather of PH^, seeing they were self-igniting, 

 than of CHj ? Yours truly, 



Hartlepool, Chables Nielsen. 



18f/( Marih, iHilS. 



[Mr. Nielsen is mistaken in assuming that the gas in the 

 Gubitz forest was self-igniting. He will know from his 

 own experiment that the flame of CH^ is often so faint by 

 day as to be invisible, but it becomes visible by night. — C. 



Tomlinson.] 



* 



ASTROXOMY ANB SIIAKSPEAEE. 

 To the Editor of Knowledge. 



Sir,— The suggestion put forward by Mr. H. M. Collison, 

 as to the " seven stars " mentioned by Shakspeare being 

 " Charles' Wain," seems probable. I have on two or three 

 occasions heard the "Great Bear" spoken of by people 

 ignorant of astronomy as the "seven stars"; and only 

 recently on pointing out to a person the Pleiades as the 

 " seven stars," he asked me if " they were a guide to the 

 pole star, as he had always understood that the ' seven 

 stars ' enabled one to find it." The persons to whom I 

 have referred were each of provincial birth and upbringing, 

 and probably came from parts of England where the old 

 name still survives. In America the commonplace name 

 for " Charles' Wain " is " the Dipper," but the most 

 curious name I have heard applied to it is " the Butcher's 

 Cleaver." The same individual asked me whereabouts in 

 the sky he could look for the " Yard Measure." I assumed 

 at the time that he meant the three stars in the belt of 

 Orion. Yours faithfully, 



Forest Gate, E. B. J. Hopkins. 



•— 



THE STRUCTURE OF THE GALAXY. 

 To the Editor of Knowledge. 



SiK, — According to Professor Pickering, the stars m the 

 Galaxy are rated about one-fifth of a magnitude too low 

 (on the average) in eye-estimates on the subject. He 

 ofl'ers no explanation of this fact, but it seems to me to 

 follow naturally from the brightness of the background on 

 which these stars are projected. According to Professor 

 Kapteyn, a star in the Galaxy is photographically brighter 

 than a star of equal magnitude elsewhere — the difference 

 between the photometric and photographic magnitudes 

 diminishing as we pass outwards from the centre of the 

 Galaxy. This seems to be a dift'erent statement of the 

 same fact. If a galactic star, rated at G-0, is really of 

 magnitude 5-8, we may expect to find it photographically 

 on the 5-8th magnitude. 



We have as yet only one-half of Mr. Marth's list of the 

 galactic latitudes and longitudes of stars up to the 6th mag- 

 nitude. Few of the stars in his list have a galactic latitude 

 of more than 20'' or 25°. But as the result of a rough 

 comparison of the stars lying within 20° of the Galaxy on 

 either side, I cannot find either that there is any clustering 

 of these stars round the galactic circle or that there is 

 any material difl'erence in the relative proportion of SLrian, 

 Capellan, and Arcturian stars throughout this region. 

 The inference appears to be that, whatever the structure 

 of the Galaxy may be, almost all the stars brighter than 

 the 6th magnitude lie on this side of it, and as the Draper 

 Catalogue is not to be relied on for stars much below that 

 magnitude, our duta as to the real structure of the Galaxy 

 are at present altogether inadequate from the spectroscopic 

 point of view. Truly yours, 



March 11, 1893. W. H. S. Monck. 



[Sirian stars are bluer than solar stars and richer in the 



