Il6 THE ADDRESSES, LECTURES, ETC., OF 



must determine the direction of 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 architecture and the plastic arts. We hear also of 

 powerful mechanical contrivances which Archimedes employed for 

 lifting and hurling heavy masses ; and the books of Euclid con- 

 stitute a lasting proof of their power of grappling with the laws 

 regulating the proportion of plane and linear measurement. But 

 with all the mental and mechanical power displayed 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 the 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 combustion 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 Accademia 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 following principal 

 groups. 



