THE VELOCITY OF LIGHT. 



BY PROFESSOR FORBES. 



AMONG the instruments that may be seen in the Loan 

 Collection at present there are many that have been used 

 in those great researches that have laid the foundations of 

 physical science. It is important as much for those who 

 are engaged in teaching science as for those who investigate 

 it to study these instruments, to note their merits, to 

 observe their defects, to judge how far we are to accept the 

 results as conclusive, and to reconcile the contrary results 

 sometimes obtained by different observers, owing to their 

 having employed different forms of apparatus. It is also 

 important that those engaged in teaching physics should 

 have the opportunity of coming in contact with these in- 

 struments, and learning from those who have been employed 

 in such investigations the peculiarities of the instruments, 

 which can be learnt only by experience. 



Having been lately employed in experiments on the 

 velocity of light, I have been honoured by the request that 

 I should open this course of lectures with an account of 

 what has been done in this important inquiry, and I 

 willingly undertook the task, because the means of experi- 

 mental research employed are as instructive as they are 

 ingenious. 



This is a subject which might at first sight seem to be 

 beyond the scope of man's inquiry. But the problem has 

 been attacked by the most skilled experimenters, and has 

 been solved to an extent that does credit to the ingenuity 

 of the methods employed. 



