Adg. 25, 18f2.1 



• KNOWLEDGE - 



209 



they will go and stand boyond that boundary, in a fog, they 

 will discover the equally curious fact that their honse is 

 then just within the fog ; the explanation of which is, 

 that you can see a certain distance through an ordinary 

 damp fog much as if tKere were none, but no further" 

 Just so if you are near a particular part of the sliore on 

 what seems a perfectly clear day, you shall see the shore 

 to a certain distance — perhaps ten or twelve miles or 

 more — beyond which it is lost in haze ; but when 

 you have reached the spot which had seemed thus 

 enwrapped in mist, you find the part where before 

 the air had before seemed clear to be equally enshrouded ; 

 the reason being, as in the other case, that you can see 

 through a great quantity of air laden with light haze, j-et 

 beyond a certain distance you cannot see ; and by a delu- 

 sion, common to all cases of vision through clouds, the 

 haze, which is really very thin, and really lies along the 

 whole space between the eye and a distant object or land- 

 scape, seems to be thick, close to, and around the object or 

 landscape which it hides or nearly hides from view. Aiding 

 this illusion, of course, if not playing the chief part in 

 causing it, is the delusion we are now considering, as to 

 the true shape of the atmospheric region above our natural 

 horizon. 



Let us, for instance, consider the question of the general 

 haziness towards the horizon. Consider a layer of air one 

 foot thick, throughout which a very thin haze is spread, 

 so that to an eye looking squarely through the layer no 

 perceptible effect of obstruction is perceived. Overhead, 

 then, the sky is perfectly clear, so far as this particular 

 layer is concerned. Let us consider what its obstructive 

 effect will be close by the horizon, assuming that it lies at 

 a height of (roughly) an eighth of a mile above the observer, 

 who is supposed tri bave a sea horizon. Note that the lower 

 it is, the gr^^ater will be the effect, or lather the difference 

 of, effect we are considering : — Let C, Fig. 1, be the place 

 of the observer, AUB the upper surface of the layer of 



air we are dealing with, adb its under surface, and db one 

 foot. What we have to determine is the breadth Xa or 6B 

 through which the line of sight towards the horizon passes. 

 Proceeding as we did in last paper, we find (putting the 

 diameter of the earth as 8,000 miles) 



(Ac)-==DC. 8,000=1,000; and {aC)-=dC. 8,000 

 .•.(AC)=-(«C)'=AC-(.C)(AC4-Ac) = Aa.aB=Drf.S,000 

 Thus wo have the proportion — 



A«:Drf::8000:Ac 



"8000:^/1000 



:: 8000: 32:: 22.-):! roughly. 



So that the line of sight passes through 22 .5 feet of haze- 

 laden air, or roughly 71 yards, in direction CA and OB 

 instead of the one foot of such air through which it is 

 dircct«'d in looking towards D. 



But now note tliat in the case of such very thin haze as 

 occupies the air on an ordinarily clear (or even a very clear) 

 cloudless day, the most elleetive part of the haze lies much 

 nearer the ground than the eighth of a mile ; and that the 

 nearef the ground is any layer we deal with as abo\e, the 

 ^eater is the disproportion between Aa, B6, and Dd. 



Suppose, for instance, we had considered a layer also one 

 foot thick, passing at a height of oidy 40 yards, or one 

 44th part of a mile overhead. Then wo should have found 

 (AC)3=8000-^44 = 182; whence we shall have AC equal 

 to between thirteen and fourteen miles. (Note, by-tlio-way, 

 the striking circumstance that a layer of air 40 yards high 

 reaches the horizon plnne no nearer than some 13 or 14 

 miles away). This would give Aa a greater than T)d as 

 8000 is greater than about 13t, or about 59 times. So 

 that for this layer the line of sight passes through nearly 

 20 yards, instead of one foot, as it does overhead. For 

 lower layers yet, and we must remember that the layers 

 come right down even to the observer's place, the dispro- 

 portion is greater yet It follows necessarily that how- 

 ever lightly the air may be laden with haze, the observer 

 looks through a great quantity of such haze, when it is 

 directed towards the horizon. Only when the air is very 

 pure indeed, then, are the heavenly bodies near the horizon 

 seen under conditions approaching those under which they 

 are seen when high overhead. 



But the effects are still more curious when we consider 

 cloud layers, for here we have often effects of foreshortening 

 to consider, which alter a sky overhead, over which clouds 

 are scattered with wide spaces between, into a sky entirely 

 cloud covered, when we look towards or near the horizon. 



Into these effects, and others akin to them, we must 

 nest inquire. 



{To be continued.) 



A GLASS OF WINE. 



Bv Dr. F. R. Eaton Lowk, M.A. 



A GLASS of wine is not unfrequently regarded as a 

 kind of passport to new friendships, and a tenacious 

 cement to old ones. A parting " glass " is supposed to be 

 the true expression of our regret on taking leave of a friend ; 

 while another glass is the inevitable exponent of our joy 

 upon his return. 



Something akin to this highly refined and pleasing 

 custom obtains amongst uncivilised races. The simple 

 African entertains his friends with his choicest palm wine, 

 which has been stored up for festive occasions in calabashes; 

 while the Tartar, actuated no doubt by the best intentions, 

 well plies his company with the oldest arrack. 



The virtues of a glass of wine have been so highly ex- 

 tolled in some quarters, that one would suppose it to be a 

 panacea for half the ills that flesh is heir to ; while, on the 

 other hand, some writers, no doubt with equal sincerity, 

 have ascribed to its daily use some of the most terrible 

 evils that can afflict humanity. 



The object of the present paper is not to attempt tbc 

 settlement of contested points, or to enter upon the debate 

 able ground opened up by the question in its physiological 

 aspect ; but simply to see what liquids and solids we have 

 got in our glass of wine. When tlic physiological action of 

 the separate constituents is understood, it will not be dilfi- 

 cult to arrive at an approximate notion of the aggregate 

 ellect upon the human constitution. The most interesting 

 ingredient in wine is, of course, the alcohol, or the intoxi- 

 cating principle. Alcohol is one of the products of the 

 fermentation of sugar ; and this process of fermentation is 

 one which has given rise to much difference of opinion 

 amongst physicists, as it involves a phenomenon altogether 

 out of the range of chemical decomposition. Fermentation 

 has been known from the earliest ages ; but it was not till 

 yeast was examined by Fabroni, an Italian chemist who 



