364 RECENT PROGRESS IN PHYSICS. 



occasion of numerous theoretical extravaganzas, brought us back to 

 the basis of a rational treatment of the subject. Could Karsten not 

 have known of this work in drawing up the papers in the 60th volume 

 of the Annalen f 



The explanation which Karsten gives of Moser's images is altogether 

 inadmissible and may be easily refuted. He thinks that, because similar 

 images can be produced by the aid of electricity, Moser's images must 

 be of electrical origin. He thinks that ' ' if two bodies, differing in any 

 respect from each other, come in contact, an electrical current is pro- 

 duced!" and that this is the cause of Moser's images. 



The generation of an electrical current by the contact of two hetero- 

 geneous bodies, which Karsten seems to intimate in this passage, will 

 not be granted by the most zealous of the adherents of the contact 

 theory ; but granting even the existence of such a current, it could 

 not produce any image, as the researches of Kiess prove. 



That electrical tension alone, without repeated discharges between 

 the body and the plate, is not sufficient to produce electrical images 

 has been shown by Know in a paper "On electrical figures and ther- 

 mography," (Pog. Ann., LXI, 569,) in which he has proved the 

 untenableness of Karsten's view as to the electrical origin of Moser's 

 images. 



The rest of the contents of Know's memoir will be mentioned sub- 

 sequently in the proper place. 



§ 77. Electrical breath images. — Eiess placed a metal stamp on a 

 shining pitch surface, and upon the stamp a small metal weight con- 

 nected by a silver wire with the knob of the spark micrometer, receiving 

 electricity directly from the conductor of the machine, while the other 

 knob of the spark micrometer, one-half line from the first, was in con- 

 ducting connexion with the ground. 



The machine being now turned, electricity accumulates upon the 

 first knob of the micrometer and upon the stamp, until a discharge 

 takes place by the passage of a spark between the two knobs ; con- 

 tinued turning will charge and discharge the stamp anew. The 

 discharges follow more rapidly the closer the knobs of the spark 

 micrometer are together. 



After several revolutions of the machine the stamp may be removed, 

 the plate breathed upon, when a shining image of the stamp shows 

 itself on the dull ground. 



It is indifferent for the success of this experiment which electricity 

 is used. 



Such images may also be produced on glass and mica, but on these 

 substances they are often imperfect. 



The simple breath image, Riess says, in caused by repeated electri- 

 cal discharges taking place in opposite directions between the model 

 and the insulating plate. The electricity communicated to the model 

 passes over to the plate, then back to the model, when the latter is 

 discharged by the spark micrometer ; thus a motion of the same kind 

 of electricity arises, first downward and thus upward. Since the dis- 

 charges between a bad and a good conductor are never perfect, elec- 

 tricity, both of the kind used and the opposite kind, remain upon the 



