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THE POPULAR SCIENCE MONTHLY. 



conditions of the present time on the char- 

 acter of those which preceded and gave rise 

 to them. Of the many classes of problems 

 falling under these heads two are specified : 

 The one deals with the reciprocal influence 

 of man and his surroundings, showing on 

 the one hand the influence of external na- 

 ture on race, commercial development and 

 sociology, and on the other the influence 

 of man on nature, in the clearing of forests, 

 cultivation and drainage of the soil, intro- 

 duction of new plants and domestic animals, 

 and the like. The other problem deals with 

 the inferences that may be drawn from the 

 present distribution of plants and animals 

 in respect to the configuration of the surface 

 of the earth in ancient times. Thus we see 

 that the mutual relations of the different 

 sciences is the subject of a science in itself, 

 so that scientific geography may be defined 

 as the study of local correlations. 



What the Eyes see in reading. On page 

 838 of our fourteenth volume we published 

 some remarks by M. Javel on the impair- 

 ment of eyesight caused by habitual pro- 

 tracted reading. M. Javel has since pub- 

 lished some further observations on the 

 mode in which the eye " takes in " the suc- 

 cessive letters on a printed page. We are 

 not to suppose, he says, that in reading a 

 line one passes successively from the lower 

 part of a letter to the upper part, then down 

 the next letter, up the next, and so on, the 

 vision describing a wavy line. The fixation 

 takes place with extreme precision along 

 a straight line, traversing the junction of 

 the upper third of the letter with the low- 

 er two thirds. Why is this line not in the 

 middle ? Because characteristic parts of 

 the letters are more frequently above than 

 below, in the proportion of about seventy- 

 five per cent. That this is so, we can see 

 by applying on a line of typographic char- 

 acters a sheet of paper covering the line in 

 its lower two thirds, and leaving the upper 

 third exposed. We can then read the let- 

 ters almost as well as if they had not been 

 concealed in greater part. But the case is 

 very different if we cover the upper two 

 thirds of the line ; the lowest third alone 

 does not furnish sufficient for recognition. 

 The characteristic part of the letters, then, 

 is chiefly in their upper portion. M. Javel 



next compares the ancient typographic char- 

 acters with those of modern books, and 

 maintains that the latter have too much 

 uniformity, so that, taken in their upper 

 parts alone, many of them may be con- 

 founded in reading. The old letters, on the 

 other hand, had each a particular sign by 

 which they could be easily distinguished. 

 The Elzevirian a, for example, has no re- 

 semblance to o, the r could not be con- 

 founded with the n, as now, nor the core 

 with o, the b with h, etc. This too great 

 uniformity in the upper part of typographic 

 characters should be corrected, since it is 

 to that part we chiefly look in reading. 



Professor Vanghan on the Origin of the 

 Asteroids. It is to the general features of 

 the numerous small planets beyond Mars 

 that we must look for a record of their 

 past history. Though most liable to elude 

 the search of the observers, asteroids of 

 great orbital inclination to the ecliptic show 

 already such numbers as to prove a stum- 

 bling-block to the usual methods of inquiry 

 respecting the primitive condition of the 

 planetary group. If, as Laplace suppose?, 

 they are parts of a ruptured solar ring, they 

 could never deviate far from the plane of 

 Jupiter's orbit by the attractive influence of 

 other planets, and the greatness of the de- 

 viation as well as its independence of size 

 excludes the idea of its arising from any 

 mutual action exerted among themselves. 

 The hypothesis of Olbers fails also to meet 

 the difficulty. In the explosion of a single 

 planet moving in the plane of the ecliptic, 

 such an impulse as produced the great in- 

 clinations of the paths of Pallas, Euphro- 

 syne, Gallia, Electra, or Artemis, would give 

 cometary orbits to masses launched forth 

 in opposite tangential directions, and cause 

 many asteroids of such an origin to wander 

 far beyond the zone between Mars and Jupi- 

 ter. Yet the peculiarities in question are 

 precisely such as may be expected in a group 

 of bodies owing their birth to a collision of 

 two planets not very unequal in size or mass. 

 Such an event would be possible when by 

 long disturbance the orbits of both become 

 too eccentric for safety, and when the aphe- 

 lion of one was in conjunction with the 

 perihelion of the other and near the inter- 

 section of their planes. Supposing both or- 



