94 PETER GUTHRIE TAIT 



GLENLAIR, 



DALBEATTIE, 



25 June 1877. 

 Art. 770 



The mounted disk of ebonite 



Has whirled before nor whirled in vain, 

 Rowland of Troy, that doughty knight, 



Convection currents did obtain 1 

 In such a disk, of power to wheedle 

 From her loved north, the pensile needle. 



'Twas when Sir Rowland, as a stage 



From Troy to Baltimore, took rest 

 In Berlin, there old Archimage 



Armed him to follow up this quest 

 Right glad to find himself possessor 

 Of the "irrepressible professor 8 ." 



But would'st thou twirl that disk once more? 



Then follow in Sir Rowland's train 

 To where in busy Baltimore 



He rears the bantlings of his brain ; 

 As he may do who still prefers 

 One Rowland to two Olivers 8 . 



But Rowland, no, nor Oliver, 



Could get electromotive force 

 [Which fact and reason both aver, 



Has change of some kind as its source] 

 Out of a disk in swift rotation 

 Without the least acceleration. 



But with your splendid roundabout 



Of mighty power, new hung and greasy, 



With galvanometer so stout, 



Some new research would be as easy 



Some test which might perchance disclose 



Which way the electric current flows. 



Take, then, a coil of copper pure 



And fix it on your whirling table, 

 Place the electrodes firm and sure 



As near the axis as you're able 

 And strive to learn the way to work it 

 With galvanometer in circuit. 



1 Berlin Monatsberichte. 



' Sylvester's address to Johns Hopkins. 



8 Heaviside and Lodge. 



