2 54 POPULAR SCIENCE MONTHLY. 



Ilaiij investigated the field witli mueli diligence, and succeeded in 

 cataloguing a large number of natural crystals by the side of tourma- 

 line. The subject was amplified later by Sir David Brewster, who 

 added a series of artificial crystalline salts to the list of pyro-electrical 

 materials, among them, notably, hydro-potassic (and sodic) tartrate. 

 The property was found not always to reside on these substances, but 

 to be developed by heating them. Brewster found that even pow- 

 dered tourmaline exhibited opposite electrifications on the opposite 

 extremities of each tiny particle, causing the latter to act, so far as 

 attractions and repulsions went, as infinitesimal magnets. 



Our rapid and imperfect survey has now brought us to the 

 threshold of the great activity in electrical work elicited by the tre- 

 mendous discovery, made by Professor Oersted, of Copenhagen, of 

 the existence of the electro-magnetic field. It happens that two of 

 the most amiable and estimable individuals that have ever devoted 

 their lives to scientific research stand out in this connection head and 

 shoulders above all other investigators — Ampere and Faraday, the 

 latter sixteen years younger than the former and destined to long 

 survive him. 



WINGLESS BIRDS. 



Br PHILIPPE GLANGEAUI), 



IT is often said that there are no rules without exceptions. We 

 purpose to test the truth of this maxim once more. Fishes are 

 made to live in water, but some of them pass the greater part of 

 their existence in mud. Some even perch upon trees, thus com- 

 peting with birds, whose kingdom is the air, and which are able, 

 Avith the aid of their wings, to plunge into space and travel rapidly 

 over considerable distances. Yet there are birds, deprived by 

 Xature, which do not possess the wing characteristic of the feath- 

 ered tribe, and are consequently, like the majority of animals, 

 pinned to the soil. 



Birds do not all have equal power of flight, which is closely re- 

 lated to the extent of the development of their wings. There exist 

 all grades in the spread of wings between that of the condor, which 

 is four times the length of the body, whereby the bird is able to 

 rise to the height of nearly twenty-five thousand feet, and the 

 little winglets of the auk, which are of no use to it. The pen- 

 guins have still smaller wings, which are nothing more than short, 

 flattened stumps, without proper feathers and covered with a fine, 

 hairlike down which might be taken for scales. 



Another group of birds exists, called appropriately Brevipennes, 



