If one approaches very cautiously so as not to be observed, a large “dog-town” presents a very curious sight. A happy, animated scene stretches away as far as the eye can see. Little prairie-dogs are found everywhere, on the top of their mounds, sitting up like squirrels, waving their tails from side to side and yelping to each other, until a most cheerful-sounding concert is produced. If you listen carefully, as you draw nearer, however, you will notice a different tone in the calls of the older and more experienced animals, and that is the warning signal for the whole population to disappear from view into their burrows. Then, if one hides quietly in the background and waits patiently for some time, sentinels will mount up to their posts of observation on top of the mounds and announce that it is safe to come out of their burrows and play about again, as the danger is past. What is Spontaneous Combustion? Spontaneous combustion is the burning of a substance or body by the internal development of heat without the application of fire. It not infrequently takes place among heaps of rags, wool and cotton when sodden with oil; hay and straw when damp or moistened with water; and coal in the bunkers of vessels. In the first case, the oil rapidly combines with the oxygen of the air, this being accompanied by great heat. In the second case, the heat is produced by a kind of fermentation; and in the third, by the pyrites of the coal rapidly absorbing and combining with the oxygen of the air. The term is also applied to the extraordinary phenomenon of the human body, which has been told of some people, whereby it is reduced to ashes without the application of fire. It is said to have occurred in the aged and persons that were fat and hard drinkers, but most chemists reject the theory and altogether discredit it. The Story in the Talking Machine[3] As far back as 1855 inventors were experimenting with talking machines; but nothing practical was accomplished till 1877, when Thomas A. Edison constructed a primitive machine capable of recording and reproducing sounds. In the early Edison phonograph the sound vibrations were registered on a tinfoil-covered cylinder. Busy with other inventions, he postponed developing the idea of a talking machine; and meantime other brains were at work on the problem. [Illustration: FIRST PRACTICAL TALKING MACHINE] [Illustration: ONE OF THE EARLIER TYPES OF SPRING MOTOR GRAPHOPHONES]