220 PROGRESS OF SCIENCE. 



with limbs of equal length(?) as with limbs of unequal length, 

 pointing out also that air-pressure is the principle of its action. 



1653 1716. Sauveur was the first after Galileo who 

 studied musical acoustics, by calculating MUSICAL VIBRATIONS 

 of particular notes by means of organ pipes of different 

 lengths and stringed instruments. From these experiments 

 and later ones made by Daniel Bernouilli (1700 1782), 

 Euler, and Lagrange, it was ascertained that the sound 

 emitted by a stretched string depends upon its tension, 

 length, thickness, and weight, and any alteration in any of 

 these conditions will necessarily determine a different number 

 of vibrations and hence cause a different note to sound. 



1678 1709. Stancari computed the number of vibrations 

 of a string emitting musical sounds thereby contributing also 

 to advance ACOUSTICS and place that branch UPON SCIENTIFIC 

 FOUNDATIONS. 



1686 1736. Fahrenheit invented a mercury THERMO- 

 METER divided into 212 freezing point being at 32 and 

 boiling point at 212. Reaumur's thermometer is divided 

 into 80, from freezing point o to boiling point 80. Celsius 

 (1701 1744) invented one, now universally used by scientific 

 men on account of its convenient simplicity, which is called 

 Centigrade thermometer, because it is divided from freezing 

 to boiling points into exactly 100. 



1692 1761. Muschenbroeck invented (1746) the LEY- 

 DEN JAR, wherein electricity was accumulated (bottled-up) 

 like a fluid a great stride ; invented also the pyrometer for 

 measuring high temperatures. 



170661. Dollond invented ACHROMATIC TELESCOPES 

 ( 1 757)- C. M - Hall had shown as early as 1729 that a 

 crown-glass lens and a flint-glass lens acting together blend 

 their coloured rays into white light. Achromatic telescopes 

 and microscopes were a great improvement, the coloured 

 edges around the objects viewed now disappearing. 



1706 90. Franklin demonstrated the influence of pressure 

 upon EBULLITION by an experiment which bears his name : 

 an increase of air-pressure raises the boiling point and a 

 diminution of pressure decreases it ; hence THE LAW " The 

 temperature of ebullition, or boiling point, increases with the 



