22 LIGHT SCIENCE FOR LEISURE HOURS. 



a summer thunder-storm. We were getting thoroughly 

 tired out, and the hcec olim meminissejuvabit with which 

 we had been comforting ourselves began to lose its 

 force. When .at length we yielded, we learned that 

 we had gone many miles out of our road, and we did 

 not reach home till several hours after dark. How it 

 fared with our schoolfellows we know not, but a result 

 overtook ourselves personally, for which there is no 

 precedent, so far as we are aware, in the records of 

 exploring expeditions. Also the offending compass 

 was confiscated by justly indignant parents, so that for 

 a long while the cause of our troubles was a mystery 

 to us. We now know that instead of pointing due 

 north, the compass pointed more than 20 towards the 

 west, or nearly to the quarter called by sailors north- 

 north-west. No wonder, therefore, that we went astray 

 when we followed a guide so untrustworthy. 



The peculiarity that the magnet needle does not, in 

 general, point to the north, is the first of a series of 

 peculiarities which we now propose briefly to describe. 

 The irregularity is called by sailors the needle's varia- 

 tion) but the term more commonly used by scientific 

 men is the declination of the needle. It was probably 

 discovered a long time ago, for 800 years before our 

 era the Chinese applied the magnet's directive force to 

 guide them in journeying over the great Asiatic plains ; 

 and they must soon have detected so marked a peculi- 

 arity. Instead of a ship's compass, they made use of a 

 magnetic car, on the front of which a floating needle car- 

 ried a small figure, whose outstretched arm pointed south- 



