POPULAR MISCELLANY. 



509 



and within the same months, 928 auroras 

 were seen in Europe or America which were 

 invisible in Finland. These statistics fur- 

 ther serve to show the geographical distri- 

 bution of auroras, which is as follows: The 

 zone of greatest frequency and intensity be- 

 gins near Barrow Point (latitude 72 north), 

 on the northern coast of America ; thence it 

 passes across the Great Bear Lake toward 

 Hudson Bay, which it crosses at latitude 60 

 north, passing over Nain on the coast of 

 Labrador, keeping south of Cape Farewell. 

 Its further course is between Iceland and the 

 Faroe Isles, to the vicinity of North Cape 

 in Norway, and thence into the Arctic Sea. 

 Thence it probably passes round Nova Zem- 

 bla and Cape Isheljuskin, approaches the 

 north coast of Asia in the eastern part of 

 Siberia, in the longitude of Nizhni Kolymsk, 

 and thence returns to Barrow Point. 



Analogies of Plant and Animal Life. 



Some very interesting analogies of plant and 

 animal life are pointed out by Mr. Francis 

 Darwin in a recent lecture. In the first 

 stage of individual existence the egg or the 

 germ the analogy is perfect ; it is no less 

 so in the stage just succeeding. Among 

 animals there are great differences as to the 

 degree of development attained by the young 

 ones before they enter the world. For in- 

 stance, a young kangaroo is born in a com- 

 paratively early stage of development, and 

 is merely capable of passive existence in its 

 mother's pouch, while a young calf or lamb 

 soon leads an active existence. Or com- 

 pare a human child, which passes through so 

 prolonged a condition of helplessness, with a 

 young chicken, which runs about and picks 

 up grain as soon as it quits the shell. As 

 analogous cases among plants Mr. Darwin 

 cites the mangrove and the tobacco-plant. 

 The ripe seed of the mangrove is not scat- 

 tered about, but remains attached to the eap- 

 sule still hanging on the mother-plant. In 

 this state the seeds germinate and the roots 

 grow out and down to the sea-level, and the 

 plant is not deserted by its mother until it 

 has got well established in the mud. For 

 the conditions of life against which the young 

 mangrove has to make a start are unfavor- 

 able enough. The most intrepid seedling 

 might well cling to its parent on finding that 

 it was expected to germinate in soft mud 



daily flooded by the tide. Perhaps, adds 

 the author, the same excuse may be offered 

 for the helplessness of babies the more 

 complicated the conditions of life, the great- 

 er dependence must there be of offspring 

 on parent. Compare a young tobacco-plant 

 with a young mangrove. All the help the 

 seedling tobacco receives from its parent is 

 a very small supply of food. This it uses 

 up in forming its first pair of leaves, and it 

 has then nothing left by way of reserve, but 

 must depend on its own exertions for sub- 

 sistence that is to say, it must itself manu- 

 facture starch (which is the great article of 

 food required by plants) from the carbonic 

 acid in the air. In this respect it is like a 

 caterpillar which is formed from the con- 

 tents of the egg, but has to get its own liv- 

 ing as soon as it is born. 



The Construction and Erection of Light- 

 ning-Rods. Dr. R. J. Mann lately summed 

 up in a series of aphorisms the funda- 

 mental conditions to be observed in the 

 construction of lightning-rods. We have 

 not room here for the whole series, but 

 select a few of the most important. The 

 main stem of a copper lightning-conductor 

 should never be less than -fa of an inch 

 diameter ; this dimension is not sufficient 

 for a building more than eighty feet high. 

 Galvanized iron may be used instead of 

 copper, but then the diameter must be 

 greater in the ratio of 6. 7 to 2.5, the con- 

 ducting capacity of iron being to that of 

 copper as 14 to 77. A galvanized iron-rope 

 conductor should never be less than j% of 

 an inch diameter; a galvanized iron strip 

 should be 4 inches wide and \ of an inch 

 thick. A lightning-rod must be continuous 

 and unbroken from end to end. A rod need 

 not be attached to a building by insulated 

 fastenings ; metal clamps may be safely em- 

 ployed, provided the rod be of good con- 

 ducting capacity and otherwise efficient. 

 Above, the rod must terminate in metal 

 points, well projected into the air; these 

 points should be multiple and perfectly 

 sharp. The bottom of the conductor must 

 be carried down into the earth and be con- 

 nected with it by a surface-contact of large 

 extent. All large masses of metal in a 

 building should be metallically connected 

 with the lightning-rod, except when they 



