Nov. 2, 1883.] 



♦ KNOWLEDGE ♦ 



275 



sensitiveness in steering so often complained of in the 

 " Humber." 



The saddle can be raised or lowered by means of an angle 

 (l ) seat-rod, which passes through the backbone ; and the 

 height of the handle-bar is also adjustable. These additions 

 enable a man of any height to ride the same machine. 



As far as I have been able to test the machine, I like it 

 very much. Before long I hope to give it an extended 

 trial over rough roads and up and down steep hills, and if 

 I get satisfactory results I will report on them. 



PRETTY PROOFS OF THE EARTH'S 

 ROTUNDITY. 



By Richard A. Proctor. 



(Con^i?l1ied Jrovn 'page 147.) 



AM sorry that pressure of space has compelled me to 



I 



defer so long the concluding papers of the present 

 series, especially as many readers have expressed a strong 

 wish that there should be no interruption. But it seemed 



earth's surface another, equally marked and much more 

 familiar, affecting the aspect of the clouds. 



The explanation of both peculiarities is the same. 



In my papers on Clouds and their Appearance I have 

 shown how we are deceived into the idea that the clouds 

 form a sort of dome over our heads, whereas the under 

 surface of a layer of clouds, though slightly arched, is in 

 reality very nearly flat within the range of view com- 

 manded by the eye. The eye is not sensible of the much 

 greater distance separating us from the clouds near the 

 horizon than from those overhead ; and losing the effect of 

 distance we picture the cloud-surface near the horizon as 

 springing almost if not quite vertically from the earth's 

 surface, to arch over, gradually at first and more rapidly 

 afterwards, towards the point overhead. When we view 

 the under surface of clouds from a balloon situated as shown, 

 in Fig. 18, a similar effect is produced. 



But also, and for precisely similar reasons, a similar 

 effect is produced on the appearance of the earth's surface 

 below us. When we look directly down we see that the earth 

 lies far below us, the greatness of the distance being very 

 obvious and striking. On the other hand when we look 



only fair to my fellow-workers here to remember that at 

 first these papers appeared on successive weeks, and that 

 therefore this was the series to give way, when pressure 

 came, and not those which are appearing fortnightly. 



Only two points remain now to be considered, one an 

 apparent difficulty, and the other a strange illustration of 



towards the horizon, although the line of sight really is 

 depressed slightly below the horizontal direction, the de- 

 pression is not at all obvious, even when we are a mile or 

 two above the sea-level. 



Say for instance we are even so much as two miles above 

 the sea-level. Then from what has been already shown. 



Fig. 19. 



the earth's rotundity, which 1 noticed several years ago when 

 travelling by rail over the plains of Western America. 



The appearance which the earth presents when seen 

 from a balloon is peculiar, and at a first view suggests any- 

 thing but the idea of a conve.x surface such as a globe like 

 the earth might be expected to present. The earth beneath 

 the balloonist appears in fact like a gigantic basin, the rim 

 of which is the horizon all round him, wliije its deepest 

 part lies below him. Mr. Glaishcr (I refer to the eminent 

 meteorologist and aeronaut, not his logarithmic offspring, 

 the (Jlaisher of Prime Factors, to whom the expansion of 

 logarithms — Cliaracteristic One — is of more interest than 

 that of any balloon the world has yet seen) has spoken of 

 this illusion, though of course he was in no sense deceived 

 by it.* 



Fig. 18 illustrates the peculiar effect in question ; but I 

 have added to the illusion affecting the aspect of the 



* But the crafty Parallax, by quoting in his Zetetio Astro- 

 nomy Mr. Glaisher's account of the illusion, without the sequent 

 comments, cleverly leaves his readers, if he has any, to suppose that 



the depression of the visual horizon (suppose it to be a 

 sea horizon) below the true horizontal direction, corresponds 

 to the angle subtended by four miles at the distance where the 

 line of sight from a height of 2 miles touches the sea level. 

 This distance, neglecting refraction, whichreally increases it,* 

 is represented in miles by ^i x f<006, or by ^ ■ ItiOUO, or 

 by about 127 miles, and 1 miles at a distance of 127 miles 

 subtends less than 2 degrees, which to the eye appears but 

 an insignificant angle. Comparing unconsciously this slight 

 depression of the horizon, with the obvious and startling 

 depression of the earth's surface underneath his car, the 

 aeronaut is deceived into the impression that the surface 

 underneath rises up all around him to his own level or 

 nearly .so, — in other words the illusion of a basin-shaped 

 depression such as is shown in Fig. 18 is produced. 



Mr. Glaislier thinks the earth may liave a concave surface, — so that as 

 tlio astronomer liolils the eartli to be convex while the aeronaut — 

 thus niisrc^prfSfMti'd— holds it to be concave, the flat-earth folk feel 

 justiliod in striking a hapjiy mean and considering it to bo as flat as 

 flat may be. 

 • Taking it into account would strengthen theargument. 



