THE SAFETY-LAMP. 



long-continued frost, is followed by a change of wind, and a thaw 

 and rain ; but after a continued frost, a rise of the mercury is 

 usually followed by snow. 



6. No rapid fluctuations of the mercury are to be taken as indi- 

 cations of any change of long continuance. It is only the slow, 

 steady, and continuous rise or fall, that is to be attended to as 

 such a prognostic. 



7. A rise of the mercury late in the autumn, after a long 

 continuance of wet and windy weather, generally indicates a 

 change of wind towards the north, and approaching frost. 



THE SAFETY LAMP. 



1. Introductory observations. 2. Fire-damp Sir Humphry Davy invents 

 the Safety Lamp. 3. Nature and laws of flame investigated and 

 discovered by Mm, and rendered subservient to his invention. 



1. AB.T often presses into its service the discoveries of science, 

 but it sometimes provokes them. Art surveys the fruit of the 

 toil of the philosopher, and selects such as suit her purposes ; but 

 sometimes, not finding what meets her wants, she makes an appeal 

 to science, whose votaries direct their researches accordingly to- 

 wards the desired object, and rarely fail to attain it. 



One of the most signal examples of the successful issue of such 

 an appeal presents itself in the safety-lamp. 



2. The same gas which is used for the purposes of illumination 

 of our cities and towns (and which, as has been stated, is obtained 

 from coals by the process of baking in close retorts), is often 

 spontaneously developed in the seams of coal which form the 

 mines, and collects in large quantities in the galleries and work- 

 ings where the coal-miners are employed. When this gas is 

 mingled with common air, in a certain definite proportion, the 

 mixture becomes highly explosive, and frequently catastrophes, 

 attended with frightful loss of life, occur in consequence in the 

 mines. The prevalence of this evil became so great, that govern- 

 ment called the attention of scientific men to the subject; and the 

 late Sir Humphry Davy engaged in a series of experimental 

 researches with a view to the discovery of some efficient protection 

 for the miner, the result of which was the now celebrated safety- 

 lamp. 



3. Davy first directed his inquiries to the nature and properties 

 of flame. What is flame ? was a question which seems until then 

 never to have been answered or even asked. 



188 



