SCIENCE, INVENTION, DISCOVERY. 



861 



propagation of energy by a wave motion 

 through this fluid a process exactly anal- 

 ogous to the transmission of sound in air and 

 of waves in water. This theory explains the 

 nature of radiant heat also and its relation to 

 light, considering it is an undulatory motion, 

 in this same ether, of similar character but 

 different degree. The now discarded corpus- 

 cular theory, which was supported by no less a 

 man than Sir Isaac Newton, assumed that an 

 infinite number of minute material particles 

 emanated from a luminous body, and, imping- 

 ing on the eye, gave the sensation of light. 

 Huygens has the credit of having propounded, 

 developed, and illustrated the undulatory 

 theory. His propositions and conclusions were 

 finally and fully substantiated by the succes- 

 sive experiments and demonstrations of Young, 

 Fizeau, and Foucault. The velocity of light, 

 or the rate at which this wave motion is com- 

 municated through the ether, is 186,000 miles 

 a second. 



Vaccination, as a preventive of small- 

 pox, was discovered by Dr. Edward Jenner, an 

 English physician. His attention was directed 

 to the subject upon casually hearing that per- 

 sons engaged in milking cows frequently had 

 the cowpox, a mild disorder of the eruptive 

 kind appearing on the udder of the animal, 

 and communicated in a similar form to the 

 hands, and that the belief was common among 

 the agricultural classes that whoever had taken 

 the disease was secure against the infection of 

 smallpox. After frequent experiments he 

 ascertained that only one form of the eruption 

 on the cow's udder possessed this property, a 

 number of these experiments being made upon 

 his son, a boy six years old. He labored 

 against opposition for many years before the 

 value of his discovery was acknowledged by 

 the medical profession. There are several 

 places in the United States where a business is 

 made of supplying the market with "vaccine 

 points" small quills, with a coating of the 

 cow virus on the ends. The name is derived 

 from vacca, meaning a cow. 



Vacuum. This word means, literally, 

 empty space, or space wholly devoid of matter. 

 Tn this sense, the results of modern scientific 

 investigation tend to prove that a vacuum can- 

 not exist, as all space is pervaded by the im- 

 ponderable elastic fluid called ether, whose 

 existence must be allowed to explain the trans- 

 mission of light and heat from distant lumi- 

 nous bodies. (See Undulatory Theory of 

 Light.) In common language, a vacuum 

 (more or less perfect) is said to be produced 

 when ordinary ponderable matter, as air, has 

 been removed from the interior of a closed 

 vessel. Until the beginning of the present 



century the most perfect vacuum that could be 

 obtained was what is called the Torricellian 

 vacuum i. e., the space above the mercury 

 in a carefully filled barometer tube. Such a 

 vacuum is, however, almost useless for experi- 

 mental purposes ; and, besides, it contains 

 mercurial vapor. By modern scientific meth- 

 ods and appliances a vacuum may be obtained 

 in which there is left less than 1-135,000 of the 

 original volume of air. An ordinary air-pump 

 in good working order will remove all but 

 about 1-120 of the air in the receiver. The 

 old phrase that "Nature abhors a vacuum," 

 was used to account for various phenomena in 

 the past among them the rise of water in 

 pumps. Most of these are now well under- 

 stood, the simple natural laws governing them. 

 Water, for instance, rises in a tube, when the 

 air is exhausted above it, owing to the pres- 

 sure of the atmosphere on the open surface of 

 the liquid in which the end of the tube is im- 

 mersed. This pressure or weight of the at- 

 mosphere is equal to the weight of a column 

 of water about thirty-two feet high, and, ac- 

 cordingly, will raise the water to this height. 

 Velocity. The average velocity of various 

 bodies is here given : 



Per hour. 

 3 miles, or 



20 



A man walks 



A horse trots 



A horse runs 



Steamboats move 18 



Sailing: vessels move 10 



Slow rivers flow 3 



Rapid rivers flow 7 



A moderate wind blows 7 



A storm moves 36 



A hurricane moves 80 



A rifle ball moves 963 



Sound moves 743 



Light moves 192,000 miles per second. 



Electricity moves '288,000 



Per sec. 

 4 feet. 

 10 

 29 

 26 

 14 

 4 

 10 

 10 

 52 

 117 

 1,466 

 1,142 



Violin. The origin of the violin can be 

 traced back to a stringed instrument called the 

 ravanastron, invented, it is believed, in 5000 

 B. C., by Ravana, King of Ceylon. The 

 crwth, which was in use in Wales long before 

 the sixth century, and to which the Anglo- 

 Saxons gave the name of fythel, whence our 

 fiddle, was a similar instrument. The violin 

 of modern form was not made until the fifteenth 

 or sixteenth centuries, and its earliest maker 

 was Gaspard di Salo, of Lombardy ; and the 

 Italian school of violin-making was probably 

 founded by him at Brescia. These Brescian 

 instruments that is to say, those made by 

 Giovanni Paolo Magini, still hold a place 

 among the best ever made. It was not long, 

 however, after the establishment of the Bres- 

 cian school when the makers of Cremona be- 

 gan to produce instruments which have been 

 objects of wonder and admiration from their 

 time to the present. The three greatest Crem- 



