32 Experimental Philosophy. [Lecture 3. 



same size and number of teeth as the wheel c. 

 On the axle of g is fixed the bar magnet qq, and 

 they turn together. Over this axle (but inde- 

 pendent of it) is fixed a point in the top of the 

 box for th^ loose needle xx to turn upon, and 

 which is the centre of the pasted circle F. In 

 the compartments of this circle are written an- 

 swers to the questions asked in the compartments 

 of the circle G. A circle of strong paper, of the 

 size of F, should cover the pasted circle, and 

 turn easily on the centre ; it should have one of 

 the triangular pieces cut out, in order to see the 

 answers. If then the needle xx is taken off its 

 point, and a person wishes to ask some of the 

 questions on the carton G, the person must turn 

 the index to the question, and then place the 

 needle on its point, giving it a whirl round, when 

 it will stop over the answer. The open part of 

 the loose circle being turned to that place, will 

 exhibit the answer. 



Itinerant jugglers often attract considerable 

 notice by exhibiting a number of these experi- 

 ments ; and there are several very amusing toys 

 constructed upon magnetic principles, and sold 

 in the shops of the makers of mathematical in- 

 struments. 



After all, however, the theory of magnetism 

 is but imperfectly developed ; nor, indeed, have 

 its leading phenomena been very cautiously traced. 

 Very imposing formulae have been published, 

 especially by continental mathematicians, includ- 



