THE REDE LECTURE 251 



and integrate, and solve all manner of regulation problems in mathematics, and 

 yet be no mathematicians. Machinery can be made to do all that sort of thing 

 better than any human being can. You must have risen far above the mere efforts 

 of memory, and of " rule of thumb," before you can consider yourselves educated. 

 Your minds must be able to do something which no machine can do for them ; 

 otherwise they sink below the level of a machine, for it is absolutely free from human 

 liabilities to error. 



But there is no cause for dread less extended education should promote same- 

 ness in opinions or pursuits a thing in itself undesirable. Unless human knowledge 

 were complete, there could not but be serious differences of opinion, even amongst 

 the most highly educated, and even on subjects of the gravest importance. Yet, 

 though extensive differences of opinion cannot but exist, you must not on that 

 account think it of little moment what opinions you hold. Every human being who 

 has received the priceless gift of reason is righteously responsible for its employment 

 to the uttermost in all the varied circumstances of life. Opinions held lightly or 

 on insufficient grounds will never be of much use in inciting to, or in directing, action. 

 " Let every man be fully persuaded in his own mind," 



On May 24, 1873, Tait delivered the Rede Lecture in the Senate House, 

 Cambridge, choosing for his subject the Thermoelectric Diagram. A fairly 

 full abstract was published in Nature, Vol. vin, and is reprinted as No. xxvui 

 in the Scientific Papers. An enlarged diagram showing the positions of the 

 lines of the more interesting metals was specially prepared, being drawn in 

 such a way as to give at a glance the Centimetre-gramme-second values of the 

 various quantities involved electromotive power, Peltier Effect, Thomson 

 Effect, etc. This was subsequently shown at the South Kensington Loan 

 Exhibition of Scientific Apparatus. 



In the preparations for the Rede Lecture, Maxwell gave valuable help, 

 as may be gathered from the following letter, written in reply to questions 

 from Tait. 



ii SCROOPE TER. 



10 March, 1873. 



O T, 



</>o/3 AXXe?. 



(1) I have no Assistant. If I can do you any service, well and good, if not, 

 why not ? 



(2) Prof. Liveing will lend you his bags, give you his gases, and furnish you 

 with lime light. If you are particular about your lantern bring it yourself, like Guy 

 Fawkes or the man in the Moon. The gases will go for half an hour. If you want 

 them for longer, say so. Bring your own galvanometer. 



(3) Thermopylae exist, but Peltier only in the form of a repulsive electrometer, 

 and the effet Thomson is an " effet defective." 



322 



