554 



NA TURE 



[Oct. 5, 1882 



angle of 104", while the telescope's magnifying power is 

 1 5 J . The definition of the prisms had been previously 

 tested on bright hydrogen lines in a dark field, and found 

 to be admirably perfect, much to the credit of their 

 maker, Mr. Adam Hilger. 



Take it all in all, nothing less powerful should be 

 employed in critical researches ; and as these prisms give 



together a dispersion of 24 between A and H, the pictures 

 they offer, with the further assistance of the telescope, 

 have a physiognomy comparable at once with either 

 Angstrom's or Kirchhoff's standard solar spectrum maps, 

 so universally respected over the whole world. 



C. Piazzi Smyth 

 Astronomer Royal for Scotland 



ELECTRIC NAVIGATION 



THE idea of propelling a boat through water by the 

 motive power of electricity is no new one. The in- 

 vention of the electromagnet showed the power of an 

 electric current to produce a mechanical force. It was 

 no very difficult matter, therefore, for the electricians of 

 fifty years ago to utilise the force of the electromagnet to 

 drive small electromagnetic engines ; and from the small 

 beginnings of Dal Negro, Henry, Ritchie, and Page, grew 

 up a group of electric motors which only awaited a cheap 

 production of electric currents to become valuable labour- 

 saving appliances. Nor was it a very long stride to fore- 

 see that if a sufficiently powerful battery could be 

 accommodated on board a boat, it might be possible to 

 propel a vessel with electromagnetic engines drawing their 

 supply of currents from the batteries. This suggestion — 



one of the earliest, indeed, of the many applications of 

 the electromagnet — was made by Prof, Jacobi of St. 

 Petersburg, who, in 1S38, constructed an electric boat. 

 Fig. 1, which we here reproduce from Hessler's " Lehr- 

 buch der Technischen Physik," represents the rude 

 electro-magnetic motor or engine, which Jacobi devised 

 for the driving of his boat. Two series of electro-magnets 

 of horse-shoe form were fixed upon substantial wooden 

 frames, and between them, centred upon a shaft which 

 was connected to the paddle-wheels, rotated a third 

 frame, carrying a set of straight electro-magnets. By 

 means of a commutator made of notched copper wheels, 

 which changed the direction of the current at appropriate 

 intervals, the moving electro-magnets were first attracted 

 towards the opposing poles, and then, as they neared 

 them, were caused to be repelled past, so providing a 

 means of keeping up a continuous rotation. This 



-The Engine of Jacobi's Electric Boat, 183S 



machine was worked at first by a Daniell's battery of 

 320 couples, containing plates of zinc and copper, 36 

 square inches each, and excited by a charge of sulphuric 

 acid and sulphate of copper. The speed attained with 

 this battery did not reach so much as 1} miles per hour. 

 But in the following year, 1839, tae improvement was 

 made of substituting 64 Grove's cells, in each of which 

 the platinum plates were 36 square inches in area. The 

 boat, which was about 28 feet long, j\ broad, and not 

 quite 3 feet in depth, was propelled, with a convoy of 

 fourteen persons, along the River Neva, at a speed of 

 2j (English) miles per hour. 



A second attempt at electric navigation was made on a 

 much smaller scale about two years ago by M. G. Trouve', 

 the well-known manufacturer of electric apparatus, of 

 Paris, who constructed an electric skiff, in which he 

 placed one of his small and compact motors, and drove it 

 by means of a battery of Planters accumulators, pre- 

 viously charged. 



The Neva and the Seine having been respectively the 

 scenes of the first and second efforts at electric naviga- 

 tion, it was fitting that the Thames should be the scene of 

 the third, and most recent one. 



The electric launch Electricity, which made its trial 



trip on Thursday, September 28, 1S82, on the waters of 

 the Thames, is certainly a great advance upon that which 

 had been previously attained. This boat, the arrange- 

 ments of which have been designed and carried out by 

 Mr. A. Reckenzaun, C.E., mechanical engineer to the 

 Electrical Power Storage Company of Millwall, is of iron, 

 and is a trifle less in length than the wooden boat which 

 Jacobi propelled. She will carry twelve persons, though 

 at the trial trip but four were on board. The screw- 

 propeller is calculated to run at 350 revolutions per 

 minute, the two Siemens' motors running at 950 revolu- 

 tions. The accumulators, which weigh \\ tons, are 

 calculated to supply the necessary current for seven or 

 eight hours of continuous work. 



Having been one of a privileged party of four, the first 

 ever propelled upon the waters of the river Thames by 

 the motive power of electricity, I think some details of 

 this latest departure in the applications of electric science 

 may be of interest. At half-past 3 on the afternoon of Sept. 

 28 I found myself on board the little vessel Electricity, lying 

 at her moorings off the wharf of the works of the Elec- 

 trical Power Storage Company at Millwall. Save for the 

 absence of steam and steam machinery, the little craft 

 would have been appropriately called a steam launch. 



