DARWIN. 61 



"Manual of Scientific Enquiry," published in 1849, for the 

 use of the navy and travellers generally, and edited by Sir 

 John Herschel, was Darwin's, on Geology. The explorer 

 is here taught to make the most of his opportunities 

 upon the soundest principles. The habits which the 

 author had himself formed are inculcated upon the 

 observer copious collecting, accurate recording, much 

 thinking. Nothing is omitted. Number-labels which 

 can be read upside down must have a stop to indicate 

 the right way up ; every specimen should be ticketed on 

 the day of collection; diagrams of all kinds should be 

 made, as nearly as possible, to scale. "Acquire the habit 

 of always seeking an explanation of every geological 

 point met with." " No one can expect to solve the many 

 difficulties which will be encountered, and which for a 

 long time will remain to perplex geologists ; bu, a ray of 

 light will occasionally be his reward, and the reward is 

 ample" Truly an ample reward awaited the observer 

 who could thus speak of the value of "a my of light;" 

 he certainly did, to use the concluding words of the essay, 

 " enjoy the high satisfaction of contributing to the per- 

 fection of the history of this wonderful world." 



Meanwhile Darwin had been carrying on a great re- 

 search on the very peculiar order of Crustacea, termed 

 Cirripedia, better known as barnacles and acorn shells. 

 He had originally only intended to describe a single 

 abnormal member of the group, from South America, 

 but was led, for the sake of comparison, to examine 

 the internal parts of as many as possible. The British 

 Museum collection was freely opened to him, and 

 as the importance of studying the anatomy of many 



