PREFACE. 



IN the space assigned to this book it was impossible to include, even approxi- 

 mately, all the physical data available. The object has been to make the tables 

 easy of reference and to contain the data most frequently required. In the 

 subjects included it has been necessary in many cases to make brief selections 

 from a large number of more or less discordant results obtained by differ- 

 ent experimenters. I have endeavored, as far as possible, to compile the tables 

 from papers which are vouched for by well-known authorities, or which, from 

 the method of experiment and the apparent care taken in the investigation, seem 

 likely to give reliable results. 



Such matter as is commonly found in books of mathematical tables has not 

 been included, as it seemed better to utilize the space for physical data. Some 

 tables of a mathematical character which are useful to the physicist, and which 

 are less easily found, have been given. Many of these have been calculated for 

 this book, and where they have not been so calculated their source is given. 



The authorities from which the physical data have been derived are quoted on 

 the same page with the table, and this is the case also with regard to explanations 

 of the meaning or use of the tabular numbers. In many cases the actual numbers 

 given in the tables are not to be found in the memoirs quoted. In such cases 

 the tabular numbers have been obtained by interpolation or calculation from the 

 published results. The reason for this is the desirability of uniform change of 

 argument m the tables, in order to save space and to facilitate comparison of 

 results. Where it' seemed desirable the tables contain values both in metric and 

 in British units, but as a rule the centimetre, gramme, and second have been used 

 as fundamental units. In the comparison of British and metric units, and quan- 

 tities expressed in them, the metre has been taken as equal to 39.37 inches, 

 which is the "legal ratio in the United States. It is hardly possible that a series 



