2o8 SECTION MECHANICS. 



the watercourses and important climatic results. In short, through 

 measurement he has achieved perhaps an important addition to our 

 geographical knowledge. As regards modern astronomy, this may 

 almost be defined as the art of measuring very distant objects, and 

 this art has progressed proportionately with the perfection attained in 

 the telescopes and recording instruments employed in its pursuit. 



By the ancients the art of measuring length and volume was tolerably 

 -well understood,hence their relatively extraordinary advance in architec- 

 ture and the plastic arts. We hear also of powerful mechanical contri- 

 vances which Archimedes employed for lifting and hurling heavy 

 masses; and the books of Euclid constitute a lasting proof of their 

 powers of grappling with the laws regulating the proportion of plane and 

 linear measurement. But with all the mental and mechanical power dis- 

 played in those works, it would seem strange that no attempt should 

 have been made on the part of the ancients to utilise those subtle 

 forces in nature, heat and electricity, by which modern civilisation has 

 been distinguished, were it not for their want of means of measuring 

 these forces. 



Hero, of Alexandria, tells us that the power of steam was known to 

 the Egyptians, and was employed by their priesthood to work such 

 pretended miracles as that of the spontaneous opening of the doors 

 of the temple whenever the burnt offering was accepted by the gods, 

 or, as we moderns would put it, whenever the heat generated by com- 

 bustion was sufficient to produce steam in the hollow body of the 

 altar, and thus force water into buckets whose increasing weight, in 

 descending, caused the gates in question to open. 



Unfortunately for them, the Academia de Cimento of Florence had 

 not yet presented the world with the thermometer, nor had Toricelli 

 shown how to measure elastic pressures, or there would, at any rate, 

 have been a probability of those clear-headed ancients applying the 

 power of steam for preparing and transporting the materials which 

 they used in the erection of their stupendous monuments, and for 

 raising and directing the water used in their elaborate works of 

 irrigation. 



The Art of Measuring may be divided into the folowing principal 

 groups : 



ist. That of linear measurement, the measurement of area within 



