98 



POPULAR SCIENCE I^EWS. 



[July, 1888. 



circles will appear to revolve in the same direc- 

 tion. The explanation of this peculiar illusion 

 is still somewhat uncertain. For our own part, 

 we find it impossible to look at the circles, even 

 when the paper is at rest, without having the 

 impression that the circles are moving, first in 

 one direction, and then in the other, though 

 we have never seen this appearance mentioned 

 before. 



A writer in La Nature suggests several in- 



teresting variations which maj- be given to this 

 experiment. If a spiral or rose-shaped design 

 (Fig. 2) is substituted for the concentric cir- 

 cles, the}' will also appear to rotate when the 

 paper is moved as before ; but the revolutions 

 will be in the opposite direction to the move- 

 ment of the paper. The remaining two designs 

 are intended to be copied on cardboard three 

 or four times larger than the original, and 

 rapidlj' revolved on a pin or wire passing 

 through the centre. Under these conditions 



Fig. 3 will be curiously transformed. The 

 four circles will disappear, and change into a 

 single circle the circumference of which is 

 bounded by the centres of the real circles ; 

 outside of this spectral circle numerous half- 

 circles appear. Wlien Fig. 4 is rotated on its 

 axis, the parallel lines disappear, and become 

 converted into concentric circles. 



Although the efllect is much better if the 

 designs are enlarged, the illusions can be ob- 

 served very well with those of the size given. 

 Figs. 3 and 4 can be cut out, and attached to 



the end of a pencil with a little paste, when 

 they can be readilj' rotated, and will show 

 quite clearly the transformations described 

 above. 



[Original in Popular Science News,] 

 DO BIRDS BUILD BY INSTINCT, OR REASON? 



BY SAMUEL BRAZIER. 



In his Iteign of Law, the Duke of Argyll, in 

 arguing in favor of the theoiy of intuitive ideas, 

 says: " Among the lower animals, young ones 

 taken from the litter or nest, and brought up under 

 conditions wholly removed from the teaching of 

 their parents, whether by imitation or otherwise, 

 will reproduce exactly all those habits of their race 

 which belong to their natural modes of life." How 

 much is meant by the words "exactly all those 

 habits of their race " is not clear. If it should be 

 taken to imply that young birds taken from the 

 nest when only a few days old, and left entirely to 

 their own instincts, will build nests exactly like 

 those built by their parents, it is entirely at vari- 

 ance with facts. Birds have frequently been reared 

 away from their parents, but when supplied with 

 the proper materials have never been found to 



build the style of nest peculiar to their tribe. 

 There is less foundation, in fact, than many would 

 at first be disposed to admit, for the general im- 

 pression that birds build the same kind of nest 

 from generation to generation, and are incapable of 

 building any other; their style of nest-building 

 being regarded as the gift of nature, as much as 

 the color of their plumage. 



A marked contrast is supposed to exist between 

 the building of nests by birds and the building of 

 dwellings by men. Birds are thought to build 

 by instinct, and therefore build forever on the 

 same plan, never vary, and are incapable of im- 

 provement. Man, on the other hand, builds by 

 reason, and therefore changes his style, and con- 

 tinually advances and improves. Nest-building is 

 the result of instinct, and is stationary: human 

 architecture is the result of reason, and is progres- 

 sive. These are the generally received opinions, 

 and, like many general conclusions, have been arrived 

 at without due regard to facts. So far is this wide 

 contrast between man and birds from being well 

 established, that facts seem to point to the conclu- 

 sion, that, in building their dwellings, men are as 

 much the creatures of instinct as the birds; and 

 the birds are as much governed by reason, though 

 of a lower kind, as man. Similar fact" to those 

 which lead to the belief that birds build by in- 

 stinct apply to many tribes of men, and in a degree 

 to all men; and similar facts to those which are 

 urged to show that man builds by reason, and 



therefore, under altered conditions, alters and im- 

 proves his dwellings, apply also to birds. 



Men, as a rule, build their dwellings with those 

 materials which abound most in those districts 

 where they have settled, and are easiest to use. 

 Sometimes it is a mere shelter of leaves, or a 

 hole burrowed in the earth. In tropical countries 

 where forests abound, the broad palm-leaf and the 

 bamboo afford the most convenient materials for 

 building. The Esquimaux and the Egyptian peas- 

 ant have neither palm-leaves nor bamboo: but the 

 one has plenty of snow, and the other has plenty 

 of mud; and with these they construct their dwell- 

 ings It is so among birds. The kingfisher uses 

 the bones of the fish it has eaten; the rook finds 

 roots .and fibres for its nest where it finds its food, 

 — in the ploughed fields; the lark also builds its 

 nest with grass, and lines it with horse-hair; the 

 crow finds fur and wool where it finds carrion; and 

 the swallow finds abundance of mud on tlie banks 

 of rivers and ponds, where it is attracted by a 

 plentiful supply of insect-food. A more extended 

 inquiry than is attempted here would show that in 

 the choice of materials for building, birds are gov- 

 erned as men are, partly by necessity, partly by 

 convenience, and partly by the force of long usage. 



But it may be urged that man reasons, and 

 therefore alters and improves his dwellings as 

 occasion requires. This is only partly true as 

 regards man, and it is to some extent true as regards 

 birds. In some cases men have continued to build 

 the same kind of dwelling generation after gen- 

 eration for ages. The Arab continues to live in 

 tents, as he did thousands of years ago. The 

 Patagonian continues to build a rude shelter of 

 leaves which could never have been inferior to 

 what it is to-day. The huts constructed by many 

 savage tribes of men show no more signs of im- 

 provement than the nests of birds. The mud vil- 

 lages on the banks of the Nile to-day are probably 

 no better than those which were built by the gen- 

 erations that raised the pyramids. Even the Scotch 

 crofter's cabin, the hut of the Highlander, or the 

 Irishman's turf cabin, are very much what they 

 were a thousand years ago. And savages and 

 semi-civilized tribes of men sometimes continue to 

 construct a particular kind of dwelling long after 

 any necessity for it has passed away. The Malay 

 islanders, for instance, construct very slight dwell- 

 ings with bamboo, and build them on posts a great 

 height from the ground. There is no special rea- 

 son why they should not build on the ground. The 

 probability is, that they have migrated from some 

 lake district where their ancestors were obliged by 

 circumstances to construct dwellings of this kind. 



Now, although certain races have continued to 

 build the same kind of dwelling for thousands of 

 years, it is not inferred that they build by instinct. 

 It is simply attributed to the force of hereditary 

 custom. On the other hand, because birds, feed- 

 ing on the same kind of foQd, and living under 

 similar conditions, are observed to build the same 

 kind of nest as their ancestors, it is supposed that 

 they are directed by instinct, and can never alter 

 or improve their dwellings. 



That young birds should build the same kind of 

 nest, and use the same materials, as their parents, is 

 the most natural thing in the world. It would be 

 most surprising it it were otherwise. The young 

 birds living in the nest till they grow strong enough 

 to leave it, and learn to fly, then returning again 

 and again to it, must certainly learn something of 

 its construction, and would probably often see the 

 parent birds at work repairing it. When they 

 come to want a nest of their own, they find in 

 their habitat the same kind of materials as were 

 used in the old nest. 



What ig ipore natural than that they should 



