March 3, 1887] 



NA TURE 



411 



locomotives of Field, Edison, Daft, and others, are 

 given. Several electric railroads of some magnitude 

 are at work in the States. Chapter VII. resiines the 

 subject of street railways in which storage batteries 

 are employed for driving the electric motors. The work 

 done in this country by Mr. Reckenzaun receives due 

 recognition, and Mr. Klicson's tramway engine is also 

 described. The industrial application of electric motors 

 in liurope and in America occupies the next two chapters, 

 the special form of motors devised by Profs. Ayrton and 

 Perry being noticed in the one and those of Griscom and 

 Daft in the other. Electrically-propelled boats and bal- 

 loons are treated by themselves ; so also is the subject of 

 telpherage. This subject — the transmission of freight 

 along a wire road by electricity — originated with the late 

 Prof. Fleerning Jenkin, and it has found imitators in 

 America. The twelfth and last chapter is devoted to the 

 latest American motors and motor systems, the motors 

 of Brush, Sprague, Van de Poele, and others, being here 

 described at length. 



And here we must pause to point out the one blot on 

 this otherwise excellent work : namely, that the entire 

 theory of the self- regulating motor, which was discovered 

 and worked out in 1SS2 by Profs. Ayrton and Perry, and 

 which forms the basis of their epoch-making paper read 

 in 1SS3 before the Society of Telegraph-Engineers, is 

 appropriated cu bloc, and accredited to Lieut. Sprague. 

 From p. 160 it appears that Sprague's method of securing 

 self-regulation is to use a differential compound winding ; 

 but this is exactly Ayrton and Perry's method. Evxn the 

 equation on p. 161, which is given as the Sprague law of 

 winding, is identical with the equation given on p. 367 of 

 the present writer's book (edition of 18S4) on dynamo- 

 electric machinery in the section on the theory of the 

 differential compound winding. Another matter credited 

 to Mr. Sprague by the authors is the discovery of a motor 

 which, when supplied at constant potential, runs faster 

 when the strength of the magnetic field is diminished. 

 But this is no new principle : it is an inherent law of 

 nature, common to all motors old and new, being the 

 simple converse to the equally fundamental fact that a 

 dynamo, if it is to generate a constant electromotive 

 force, must be run faster in a weak field, and may be run 

 slower if the field is strengthened. Lieut. Sprague has 

 done good work in producing motors of excellent design 

 and having points of original merit : this we may freely 

 acknowledge without ascribing to him what was known 

 before his work was begun. The authors will do well to 

 correct these slips in the second edition, which will 

 probably soon be demanded. The book is creditable 

 alike to authors and publisher. 



SiLVANUs P. Thompson 



THE FLORA OF LEICESTERSHIRE 

 riie Flora of Leicestershire, including the Cryptogams. 

 With Maps of the County. Issue! by the Leicester 

 Literary and Philosophical Society. 372 Pages and 

 2 Maps. (London and Edinburgh : Williams and 

 •Xorgate, 18S6.) 

 '■pHE county of Leicestershire covers an area of Soo 

 square miles of the centre of England, at the sum- 

 mit of drainage between three of the great streams, the 



Trent, the Severn, and the Midland Ouse. Almost the 

 whole of the county is at least 100 feet above sea-level. 

 A large portion of the surface is between 300 and 500 

 feet, and Charnwood Forest rises at its highest point to 

 900 feet, so that Leicestershire is very different from such 

 low-lying level Midland counties as Cambridgeshire, Bed- 

 fordshire, and Huntingdonshire. Half the area of the 

 county is in grass, about one-quarter is under arable 

 cultivation, and there are 20 square miles of woodlands. 

 In Charnwood Forest there are slate and granite, and the 

 sedimentary rocks are represented in the county from 

 the middle of the Palaeozoic to the middle of the Mesozoic 

 series — Carboniferous Limestone, Coal-measures (Permian 

 missed out), Trias, Lias, and Lower Oolite — so that there 

 is every variety of soil. 



Competent botanists have resided in the county for the 

 last three generations. The fathers of Leicestershire 

 botany are Dr. R. Pulteney, F.R.S., who was a surgeon 

 at Leicester, and the author of " A General View of the 

 Writings of Linnaeus" (1781), and the well-known " His- 

 torical Sketches of the Progress of Botany in England 

 up to the date of the general adoption of the Linnsean 

 System" (1790); and the poet Crabbe, who lived at 

 Belvoir from 1782 to 181 3, when he removed to Wiltshire. 

 Between 1820 and 1850 Leicestershire was the home of 

 three clergymen, all of whom were enthusiastic botanists. 

 The Rev. Andrew Bloxam lived at Twycross for more 

 than forty years. He is best known as one of the special 

 investigators of the British brambles, and partly, perhaps, 

 because he worked them so thoroughly there is a general 

 idea that Leicestershire is the richest county in England 

 in forms of this complicated genus. He was one of the 

 last survivors who kept up the old tradition of botany as it 

 was in the days of Smith, Hooker, Turner, Dillwyn, and 

 Forster, when a collector swept through the whole veget- 

 able kingdom, from the flowering plants down to the fungi. 

 The Rev. \V. H. Coleman was a most energetic and 

 capable botanist. He was for many years one of the 

 masters of the Ashby-de-Ia-Zouch Grammar School, and 

 it was he who laid the basis of the present work, dividing 

 the county into a dozen districts, and tracing out the 

 distribution of the plants through them as fully as he had 

 opportunity. He died in 1S64, and in 1S75 '^'s manu- 

 script was handed over by his friend Mr. Edwin Brown, 

 of Burton-on-Trent, to the Leicester Literary and Philo- 

 sophical Society, which appointed a Committee to amplify 

 and revise it. Of this Committee Mr. Mott, of Leicester, 

 has acted as Chairman, and Mr. Carter, Dr. Finch, and 

 Messrs. E. and C. Cooper are the other members. 

 The other clergyman who worked in conjunction with 

 Messrs. Bloxam and Coleman was the Rev. Churchill 

 Babington, for many years the Disney Professor of 

 Archfeology at Cambridge, and now Rector of Cockfield, 

 in Suffolk. In 1S50 Miss Mary Kirby (now Mrs. Gregg) 

 published a small flora of the county, which contained a 

 substantially complete list of the flowering plants and 

 ferns of Leicestershire, but no attempt was made to trace 

 out their distribution in detail. 



In the present work the number of flowering plants 

 and ferns, native and naturalised, in Britain is estimated 

 at 1546, and of these, S25 are admitted for Leicestershire. 

 This number of 1546 is reached only by counting the sub- 

 species of such variable types as Ranunculus aqualilis and 



