8 



SCIENCE-GOSSIP. 



[/an. 1, 1865. 



which again grow other fronds, and so on ad 

 infinitum. The method of growth in the three 

 other species is precisely similar, and can be 

 clearly seen in all under a magnifying power. 

 Had it been the intention of this paper to 

 embrace any account of other living organisms 

 in the aquarium, a description might have 

 been given how the tadpoles were continually 

 biting off the rootlets of the Duckweeds ; how 

 the great beetles seized the tadpoles, and bit 

 their tails off, so that they could not rise to 

 the surface ; how the tadpoles again in their 

 turn attached themselves, six or eight at a 

 time, to the sides of the carp, where they 

 hang for days together, going round and 

 round with the fish, sucking their juices, and 

 becoming veritable parasites ; how the fish 

 were continually gulping down fronds of 

 duckweed, and as quickly disgorging them ; 

 how, when the tadpoles were dead, because 

 the aquarium and the beetles would not let 

 them become frogs, the snails were the objects 

 of the beetles' fury ; and how, at length, the 

 beetles gave themselves up to unmitigated 

 cannibalism, and " did each other eat." Such 

 a description would doubtless be instructive 

 and entertaining enough to induce us to 

 return to it on some future occasion. 



W. G. S. 



WHY OBJECTS APPEAR LARGER 

 THROUGH THE MICROSCOPE. 



WHY objects under the microscope 

 appear so much larger than when 

 seen by the naked eye, is an inquiry that 

 would naturally suggest itself to the mind of 

 an intelligent lad or adult, who for the first 

 time in his life peered through the tube of 

 his friend's microscope. The answer to such 

 an inquiry will, we believe, reveal to us the 

 principle on which the microscope itself is 

 constructed. A mere speck, undistinguishable 

 either in form or colour, is placed before us. 

 Our friend transfers it to the stage of his 

 microscope, adjusts the tube, and invites us to 

 take a peep. We do so. Astonishment seizes 

 upon us. Every part of that object is clearly 

 mapped out ; every member of its body duly 

 displayed, and even a portion of its internal 

 organization is distinctly revealed. We de- 

 part to our homes mentally asking, By what 

 means such an addition of power is obtained 

 for the eye ? 



In what, then, does magnitude consist, that 

 at one time on oliject should appear large, 



and at another time small ? Let us endeavour 

 to unravel this mystery. 



It will readily be admitted that we judge 

 of size by compai-ison — we compare one 

 object with another— and thus form an idea 

 of the extent it occupies in space. But had 

 we nothing with which we could make the 

 comparison, it would be impossible to judge 

 of size at all. 



It will be found that the apparent size of 

 an object varies with the distance it may be 

 from the eye of the spectator. Thus, a 

 balloon at a great altitude, or a castle at a 

 distance, both appear vastly diminished in 

 bulk by reason of their remoteness ; and had 

 we no other means of judging their magni- 

 tude than those furnished by the eye, we 

 should unhesitatingly believe the first to be 

 no larger than a boy's top, and the latter a 

 fitting residence for a child's twopenny doll. 

 Even the sun himself, under similar circum- 

 stances, would be dwarfed to the size of the 

 crown of one's hat. Fortunately we have 

 other means at our disposal for coi-recting our 

 visual impressions. 



If the aeronaut at our bidding suddenly 

 quitted the clouds and descended at our feet, 

 we should observe his balloon gradually ex- 

 pand in every direction until it assumed the 

 dimensions of a house. A small portion of 

 the balloon contained within one of the 

 lozenge-shaped meshes of the netting would 

 appear at this short space even lai'ger than 

 the entire machine when seen from a distance. 

 So also with the castle. If we travel towards 

 it, we shall perceive it looming out larger and 

 larger, as tlae distance decreases between it 

 and ourselves. At last we stand beneath its 

 walls. We now see but a very small por- 

 tion of the building. It has so rajudly 

 increased in size that a single stone 

 covers with its image a larger space on 

 the retina of the eye than the whole struc- 

 ture when seen afar off. If, then, the mag- 

 nitude of an object depends on the distance 

 the eye of the si)ectator may be from it, 

 it ought to follow that the nearer the eye 

 the larger the appearance of the object ; and 

 this we think will be fuund to be the case. 

 There is, however, a limit to the eye in this 

 direction. In an ordinary healthy eye ten 

 inches is considered to be the distance at 

 which small objects can be most distinctly 

 seen, and this may be termed its natural 

 focus. When objects are brought nearer 

 than this they become indistinct and hazy. 

 They are then out of focus. The eye is so 

 constructed that it cannot accommodate itself 

 to a shorter distance than its natural focus 



