THE PROBABLE AGE OF THE WORLD. 651 



in favor of old acquaintances, but we liked them better before. Di- 

 gressions, perhaps, are cut out ; some little rash speculation quietly 

 withdrawn ; some hit at an opponent suppressed ; but they do not 

 always command the same ready assent, or appear so interesting as 

 they did in their old form. 



These remarks do not apply to Prof. Tait. His lectures now 

 before us, from their nature, belong to the class of composition for 

 which we avow our predilection. They were delivered extempore to 

 a scientific audience, and printed from short-hand notes. They lose 

 nothing of their vigor, to use an expression of Lord Macaulay, by 

 translation out of English into Johnsonese. We are allowed to seize 

 the thought in the making, and, if it loses anything in grace, the loss 

 is more than counterbalanced by power. 



Those who wish thoroughly to understand the subject of this 

 paper should study Prof. Tait's lectures on the souces of energy, and 

 the transformation of one sort of energy into another. Matthew 

 Arnold's phrase, " let the mind play freely round " any set of facts of 

 which you may become possessed, often recurs to the mind on reading 

 these papers. There is a rugged strength about Prof. Tait's extem- 

 pore addresses, which taken together with their encyclopedic range, 

 and the grim humor in which the professor delights, makes them very 

 fascinating. They have another advantage. Men not professionally 

 scientific find themselves constantly at a loss how to keep up with the 

 rapid advance which has characterized recent years. One has hardly 

 mastered a theory when it becomes obsolete. But in Prof. Tait we 

 have a reporter of the very newest and freshest additions to scientific 

 thought in England and on the Continent, with the additional advan- 

 tage of annotations and explanations by one of the most trustworthy 

 guides of our time. 



We propose to discuss the books and papers whose titles are pre- 

 fixed to this article, in so far as they throw fresh light on the probable 

 length of time during which the solar system may be supposed to 

 have existed. It is but in recent times that any materials have been 

 amassed for forming an opinion on the subject. Before the end of the 

 last century geology hardly existed as a science ; an inquiry as to the 

 age of the world would have been unhesitatingly answered by the as- 

 sertion that the earth was created in six days, 4,004 years before the 

 birth of Christ. Though further research has shown that the sacred 

 text bears no such interpretation, those copies of the "Authorized 

 Version of the Bible" which are enriched with notes and marginal 

 references still keep up the formal assertion. 



A story is told in Brydone's " Tour in Sicily " which will serve 

 to recall the state of public opinion on the subject of chronology at 

 the end of the last century. The CanonicoRecupero, a Sicilian priest, 

 was Brydone's guide when he explored Mount Etna. Recupero (who 

 afterward wrote a history of his native mountain) told the traveler 



