Transcriber's Notes

The following typographical corrections have been made:

[Page x]: Heat without combustion—Inter-currents{original had no hyphen; changed to match page 45, to which it refers}

[Page xiii]: The fifth plate (from the Addendum) has been added to the list of illustrations.

[Page 60]: back and forth to maintain an{comma removed} equilibrium.

[Page 64]: {quotation mark removed}The course of a balloonist

[Page 102]: {quotation mark added}"These clouds sometimes range themselves

[Page 107]: {quotation mark added}"The overwhelming probability of a common cause

The following inconsistent hyphenation is as printed:

[Page 42]: just such a retro-acting inter-communication.

[Page 72]: might interfere with the intercommunication of light