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XXIV. Notices respecting New Books. 



Tables of Physical and Chemical Constants. G. "VV. C. Kate and 

 T. H. Laby. Fourth Edition. 160 pages. (Longmans, Green 

 & Co., 1921 ; price 14 shillings.) 



r |^HE test of the utility of these Tables is the call for a fourth 

 •*- edition. Alterations and additions have been made relating 

 to the figure of the earth, acceleration of gravity, and the gravi- 

 tation constant; and the chemical data have been recalculated, 

 using the international atomic weights. 



The conventional niggling C.G.S. units are employed through- 

 out. But it will do no harm to point out certain advantages in 

 the M.K.S. system (metre-kilogramme-second), tacitly employed 

 in electrical work units more usual for commercial purposes. 



A metre cube (m 3 ) of water is here the metric tonne (t) of 

 1000 kg, and density is reckoned in kg/m 3 . 



The theoretician's objection to the M.K.S. system of making 

 1000 the density of water is a practical asset, as the last unit 

 figure of the tabulated density of a substance is then affected by 

 the density of the air, to the extent of about 1*25; the density 

 given in the table being absolute density in a vacuum, from which 

 this deduction must be made in a careful weighing carried out 

 in air actually by the human machine, and not merely the 

 mechanical balance alone. 



It is curious how this Hospifalier notation should be so long 

 in making its way into use, recommended us far back as 1883 in 

 an International Electrical Congress. Xo need then for that 

 confusing chapter on Units and Dimensions ; these are always 

 kept in view by Hospitalier. 



In the M.K.S. units the joule replaces the erg, but no name has 

 been found yet to replace the dyne, equivalent of 100,000 dynes; 

 this force would represent the weight of about 100 g, say 

 10 pennies, so it cannot be described as large, while the dyne and 

 erg are too microscopic to be used except with high powers of 

 10 in the index notation. 



In matter relating to the figure of the Earth, the circumference 

 should be stated, and the radius or diameter never be mentioned. 

 It is not right in a treatise on Trigonometry for the use of the 

 naval officer to give the radius of the Earth as about 4000 miles, 

 and then not specifying whether it is the military land mile, or 

 the nautical geographical (G) mile that is intended. Only the 

 G mile should be implied, and then the circumference of the 

 Earth is 21,600 miles, as laid down by E-oger Bacon in the Opus 

 Majus, and this makes the radius 3438 G miles, a radian arc of 

 57°'3, or 3438'. 



In the Metric System the circumference was made into forty 

 thousand kilometres ; and then in these units the slight varia- 

 tions from the true sphere are expressed in a small variation 

 from a large round number. 



