Notices respecting New Boohs. 73 



circumference : this will of course make the electric stress 

 increase more rapidly than x. When the dielectric is a 

 rarefied gas it is not broken down until the electric stress 

 exceeds a certain value: hence the discharge takes the form 

 of a luminous ring in the outside of the bulb. By increasing 

 the sparking- distance in discharging the Leyden jar the 

 magnetic induction is increased, making the electric stress 

 greater and broadening the ring. 



The breadth of the ring also depends on the degree of 

 exhaustion of the bulb ; as the value of the electric stress 

 requisite to break down the rarefied gas depends on the 

 degree of rarefaction. In the case of an annular exhausted 

 tube placed outside the coil the luminous ring will be nearest 

 to the inner side of the tube : since when x is greater than r, 

 the E.M.F. per unit of length is less the greater x, on account 

 of the lines of magnetic induction outside the coil being in 

 the opposite direction through the path x to those inside 

 the coil. 



IX. Notices respecting New Books. 



Odorograplxia, : a Natural History of Raiv Materials and Drugs used 

 in the Perfume Industry. By J. 0. Sawek, F.L.S. London : 

 Gurney and Jackson. 1892. 



IN this work by Mr. Sawer we have another illustration of the 

 intimate relation existing between science and industry which is 

 such a striking feature in the educational movement of the time. 

 No book has yet appeared in which the ground covered by the 

 present author has been traversed by any writer who has brought 

 such qualifications to bear upon the subject, and we have as a 

 result a volume which may fairly be commended as unique in its 

 way, and which will prove a boon to all interested in the chemistry, 

 natural history, and technology of the numerous materials used in 

 perfumery. 



A very brief description of the contents will suffice to show how 

 thoroughly the subject has been handled. In the first chapter, 

 devoted to musk, we have an account of civet and ambergris, and 

 a list of all the animals and plants which give this odour, together 

 with a description of the artificial musk recently introduced by 

 Baur, and obtained by the nitration of certain coal-tar hydrocarbon 

 derivatives. The second chapter, on the odour of roses, is a very 

 long one, and deals first with the true " otto of rose " manufactured 

 in Bulgaria and elsewhere, the chemistry and technology of which 

 are given in considerable detail, and illustrated by figures of the 

 apparatus used and a map of the Bulgarian rose-farm district. An 

 account of rose culture in France is also giveu, and a description 

 of other odoriferous substances resembling rose, such a* pelar- 

 gonium, and artificial rose perfumes, such as ammonium salicylate, 



