i88 5 -] 
A naly ses of Books. 
487 
wliai to look for when the necessary preparations have been 
made. Doubtless some of our makers of microscopical obiedts 
will soon bring out a series of slides in illustration, after the 
admirable manner of the late C. V: Smith, of Carmarthen : but 
students who wish really to learn had better buy or procure 
somehow only the plants and materials, doing everything else 
with their own hands. ^ s 
The present volume concludes with the ferns and their allies 
leaving the remaining Cryptogamia for the second part. 
The book is free from the pest of a collection of examination 
questions. Let us hope that the second part may also omit 
these impediments to students. J 
On the Apparent Enlargement of the Constellations , the Sun, and 
the Moon near the Horizon* By M. Paul Stroobart. 
Bruxelles : F. Hayez. 
This illusion is the more remarkable because the Moon, when at 
the horizon, is more distant from us by a radius of the Earth 
than when in the zenith, and consequently it should appear in the 
former case smaller by 0-5'. 
The author discusses the four principal hypotheses which have 
been proposed to explain this appearance. 
The first of these supposes that the luminary is magnified by 
atmospheric refradtion. 
The second, proposed by Alhazen in his “ Optics,” as far back 
as the beginning of the nth century, attributes the apparent en 
largement of the stars to the flattened form of the celestial vault, 
the base of which, according to the Arab savant, is more remote 
from us than the summit by an entire radius of the Earth. 
Hence we imagine the stars more distant from us when they are 
near the horizon than at the zenith. We know by experience 
that the more remote an objedt the smaller it appears. If, then, 
in imagination we place the Moon on a plane more distant from 
us when on the horizon than when in the zenith, we ascribe to 
her mentally a real magnitude more considerable in the first case 
than in the second. 
The third hypothesis agrees essentially with the second. When 
the stars are rising or setting we see a great number of objedts 
between them and us, which gives us a greater idea of their dis- 
tance, and consequently they appear greater. 
According to the fourth hypothesis, when the Sun and the 
* Sur l’Agrandissement apparent du Constellations, du Soleil et de laLune 
a l’Horizon. 
