234 Progress of Invention. 



down one by one, and then it is that the gull, drawing gradually 

 within reach, suddenly darts out his long neck, and seizes an un- 

 fortunate sparrow by the head. So rapidly is this done, that escape 

 for the unsuspecting sparrow is hopeless, and in another second he 

 is crushed and devoured." On one occasion this same bird seized a 

 young kitten, which the cat had brought out on the lawn, and tried 

 to swallow it whole. He was discovered with the kitten's head 

 down his throat, making frantic efforts to swallow the body, and 

 was greatly disappointed when the little creature was rescued by 

 one of the family. This book is illustrated by musical notations of 

 the song of many of the birds, and by a frontispiece in a deplorable 

 style of art. A very tolerable engraving of Kingsbury Reservoir 

 is quite spoilt by printing a dingy rhubarb tint all over it ! 



PROGRESS OP INVENTION". 



Improvement op the Hypsometer. — The boiling points of fluids 

 depend on the pressure of the air. The greater the altitude of any 

 place above the ordinary level of the earth's surface, the lower the 

 boiling point of a given fluid, because the less the barometric 

 pressure in that place. And hence the height of any place may be 

 found by means of the boiling point of water in that place. With 

 this object a peculiar kind of thermometer, termed a hypsometer, 

 ■or more correctly, a hypso-tliermometer, has been constructed. It is 

 marked, not with degrees of temperature, but with barometric 

 pressure corresponding to these degrees, or, better still, according 

 to the latest improvements of M. Abaddie, with the altitudes cor- 

 responding to the temperatures, supposing them to be the boiling 

 points of water. The boiling point of a fluid can be accurately 

 determined by placing the thermometer in the escaping vapour ; 

 but unfortunately the results are liable to vitiation, on account of 

 the tendency which the zero of thermometers almost invariably has 

 to alter spontaneously. The danger of error from this cause is, 

 however, greatly diminished, if two or three hypsometers are used 

 in each experiment, and the mean of their indications is taken. The 

 hypsometer is, for several reasons, more suitable for the purposes of 

 travellers than the barometer. It is more easily carried, it is less 

 easily injured ; and it requires, not an observation, but an experi- 

 ment which is made with greater facility, and is less subject to 

 orror. 



Magnesium and its Salts as illuminating Agents. — The com- 

 plication necessary when the magnesium wire is fed by means of 

 clockwork, has been hitherto a great obstacle to the use of the mag- 

 nesium lamp for the purposes of illumination or photography. This 

 difficulty has, however, been obviated by the lamp exhibited in 

 operation at the recent meeting of the British Association at Not- 

 tingham. The magnesium passes down in the form of a very fine 

 powder from a reservoir, through two small tubes, the lower aper- 



