440 



KNOWLEDGE. 



November, 1910. 



figures in the street on a foSK'y night, because they arc much 

 closer than imagined, will occur to most people. 



It .-eenis also quite within the limits of possibility that some 

 (>t the errors of interpretation as to the meaning of what is 

 ~een under the microscope may be due to mental suggestion. 



It will be understood that the extent of such illusions as 

 have been referred to \aries somewhat according to the 



" personal equation " of the observer, and that what has been 

 described is simply the experience of the writer, who it may be 

 of some interest to mention, has since he thought out the 

 matter, almost entirely lost the impression that the Sun and 

 Moon appear larger when rising or setting than at other times, 

 though he has been quite unable to divest himself from the 

 illusion in the case of constellations or stars. 



X-R.AV.S FOR EX AMI XI XG PETRI F.ACTIOX.S. 



Bv Dk. .\LFRKD GKADENWITZ. 



The extremel\' numerous technical and scientific uses ol 

 X-rays are Unown to be based on the differences in trans- 

 parence shown by the \'arious tissues in regard to these rays. 

 The silhouettes produced by 

 the passage of X-rays there- 

 fore give an insight into the 

 internal structure of liuui.iu 

 and animal organisms, which 

 would otherwise be for e\er 

 closed to our eyes. 



The latest achievement in 

 this connection is the use of 

 these wonderful radiations in 

 investigating the internal struc- 

 ture of fossils. In fact, a 

 French scientist, M. Pierre 

 Goby, at Grasse. has recently 

 obtained some excellent X-ray 

 pictures of petrified starfishes, 

 of which an example is repro- 

 duced in Figure 1. 



It is well known that those 

 countries which were formerly 

 covered by the sea contain in 

 their soil great quantities of 

 renmants of the ancient marine 

 fauna. To these countries 

 belong the environs of Venice 

 in Southern France, the fossil 

 treasures of which have been 

 lately investigated with especial 

 care, partly, as has been hinted, 

 with the aid of X-rays. 



In order to understand the possibility of using X-rays in this 

 connection it should be considered that all the internal 

 parts of a petrified starfish are filled up b\- a remarkalil\- 



l'}\vu a Scitigia^/l 



Clypcastcr htti 



homogeneous quart/; mass which mainly consists of an 

 agglomeration of minute transparent grains, bound together 

 by a glue so loose as to leave small cavities in the interstices. 



Though being little trans- 

 parent to X-rays, this mineral 

 mass is far less opaque than 

 carbonate of lime, the sub- 

 stance of which the shell of 

 the starfish consists. This 

 is how the X-ray picture 

 of the petrifaction, surprising 

 though this be, absolutely 

 resembles that "f a li\ ing 

 starfisli. 



.A.ny slight discontinuity in 

 the \arious portions of the 

 petrifaction will result in a 

 difference in the depth of 

 shades. The five radial grooves, 

 e.g., are distinctly visible, and 

 the thinnest portions of the 

 petrifaction, viz., those at the 

 edges, are especially clear. The 

 digesti%e tube which surrounds 

 the central cavity is seen with 

 remarkable distinctness, each 

 of its circumvolutions being 

 clearly marked. 



The naturalist recognises 

 /■!■ Pi\-rn- c.i/n: '" ^'^'^ X-ray picture a num- 

 ber of features of much im- 

 nisfris Agassis. portance from a scientific 



point of \' i e w . but which 

 cannot be discussed in the present article. 



From the above is seen that X-ray pictures are likely soon 

 to prove a powerful aid also in the work of palaeontologists. 



THE SHOOTING .ST.AR.S OF NOVEMBER. 



The mere mention of the Leonid meteors is sufficient to arouse 

 a certain amount of enthusiasm amongst meteoric observers. 

 There are many of us who remember the brilliant display of 

 November 13th. 1S66. and in many cases it nnist ha\e formed 

 the chief meteoric spectacle of a lifetime. 



There were brilliant and abundant displays of the Andro- 

 medids or meteors from Bida's comet on November 27th in 

 1872 and 1885, but these were partially \eiled by clouds at 

 Bristol, and at certain places nothing could be seen. But 

 the Leonids formed the most impressive scene everywhere. 

 They are very rapid, bright streaking meteors, and more 

 striking objects generally than the star morning meteors of 

 Bida's comet. 



It is true that observers looked in vain for a great displav of 

 Leonids in 1899 and 1900. Planetary perturbation appears 

 to have disturbed the orbit and to have been responsible for 

 the absence of the meteors. They returned, however, in fair 

 abundance in 1901 and 1903, though the numbers fell far 



below those seen in 1799, 1833 and 1866. Will they return 

 this year ? That is a question now being asked, though every 

 astronomer knows that the conditions will be unfavourable. 

 The parent comet of the swarm is now at an enormous 

 distance from the earth, but has probably left a pretty rich 

 train of meteors behind it. As a popular spectacle, however, 

 it cannot be said that the shower is likely to prove 

 remarkable ; it is more as an astronomical event and one for 

 strictly scientific observation that we call attention to it. After 

 11 p.m. on the night following the 14th and 15th a few fine 

 Leonids ought to be seen wherever the atmosphere is clear 

 enough for suitable watching. There will be no interference 

 from moonlight, so that in this respect we shall be favoured. 



In our English climate, however, fogs or clouds may quite 

 eliminate the Stars and Meteors. This has been the experience 

 on many former occasions ; but with fortunate circumstances 

 it is hoped that the Leonids will be patiently looked for and 

 successfully witnessed. w_ p- DENNING. 



