24 , TRANS. ST. LOUIS ACAD. SCIENCE. 



"For a 300-foot tape a party of sixteen persons is required, 

 distributed as follows : Observer and assistant at rear end ; ob- 

 server, assistant, and attendant, at front end ; nine (9) helpers, 

 one at each supporting-stake — two of these helpers must be able 

 to read thermometers closely and reliably ; one recorder ; one 

 chief of party as superintendent. 



"The rear observer, as soon as he sees or feels the weight ap- 

 plied, adjusts his end approximately and calls out ^ ready. ^ The 

 front observer replies ^ ready.'' The rear observer calls out 'mark. 

 The front observer replies 'marked.' 



"The thermometer-readings are then called out and recorded, 

 time and weather noted, and all stand ready to march except the 

 front observer. He makes and numbers a line on the zinc from 

 the puncture made with the engraver's pencil at right angles to 

 the base. This done, he takes the front end of the tape and gives 

 the word 'march.' All move rapidly forward carrying the tape. 

 Each helper carries the tape in its hook, ready to suspend from 

 the nail-head in the proper supporting-stake. The thermometers 

 are carried attached to a stiff wire-stake, and when read their 

 bulbs are at the elevation of the tape. The superintendent watches 

 against twist in tape and other irregularities. Second and third 

 measurements are so numbered on the zincs. Differences are 

 read to the nearest hundredth of an inch, and the elevation of the 

 marking-stakes taken before the zincs are taken up. The zincs 

 are numbered and saved for future reference. 



"In daylight a tape-length can be measured in less than two 

 minutes, or a two-mile base can be measured in an hour. By 

 lamplight one-third more time is required. Three measurements 

 are made in an afternoon and night, the one by daylight being for 

 the practice of the untrained men." 



The best measurements are made at night after an overcast day. 



The reliability of the measurements is best shown by the re- 

 sults obtained. These are for the four secondary bases measured 

 as follows, corrected for expansion of tape to 62° Fahr. : 



Benton Base {Mon.) 18S5. 



Ft. Mean Temp. 



ist measurement, by day = 9S70.304 ( 86°. 5 ) 



2d " by twilight after a heated day = .443 ( 65°.2 ) 



3d " by lamplight = .388 ( 58°.9 ) 



