7 o8 SCIENCE PROGRESS 



dealt with in Lecture V., and in addition to cold storage and ice-making machinery 

 -we find a reference to the drying of air for blast furnaces and an ample description, 

 •with illustrations, of the methods adopted for cooling magazines in war-ships. 



Lecture VI. deals with the applications of extreme cold, and the matter it 

 contains is certainly, from an engineering point of view, the best and most com- 

 prehensive treatment we have of the methods and machinery for the liquefaction 

 of "gases" and the production of very low temperatures. 



An appendix on the thermo-dynamics of liquid air would have made the 

 matter still more complete, as in the appendices we find further considerations of 

 most of the theoretical points raised in the lectures, including a most important 

 description of the use of Mollier's (j> — i and/ — i diagrams (where i = n 4- K.pv) — 

 diagrams of immense value, for instance, when dealing with the difficult questions 

 that arise when attempting the design of carbonic acid machines for use in warm 

 ■climates. 



In reading such a book one forgets there is such a thing as technical " instruc- 

 tion " and thinks only of " education," and yet not a single technical problem of 

 -any importance in mechanical refrigeration is left untouched ; and the reader, 

 whether he be a student or practical engineer, will find all he requires in this 

 volume outside of that experience and knowledge which is born only of actual 

 practice. 



The mechanical engineering student of to-day is happy in the possession of 

 three such books as Steam Engine and other Heat Engines, Strength of Materials, 

 and Mechanical Production of Cold, all by Dr. Ewing, and happier still the 

 technical institution which uses them as a basis for its own work. 



J. Wemyss Anderson. 



notices sur des plantes utiles on interessantes de la Flore du Congo. Par 

 Emile De Wildeman. [Vol. ii. fasc. ii. (1908), pp. 167—270.] 



The whole of this fascicle is taken up by an article headed: " Apocynacees. 

 Notes sur leur valeur caoutchoutifere et leur distribution dans le Congo Beige." 

 Under this somewhat misleading title the author includes notes, mostly records 

 of new localities of about thirty-five African Apocynacece, and a complete 

 •enumeration of the species of the genera Landolphia (61), Clitandra (30), and 

 Carpodinus (39). This enumeration, which covers seventy-five pages, contains 

 numerous references to the more recent literature on the subject, many new 

 distribution records, and interspersed here and there critical and sometimes rather 

 lengthy remarks on their specific characters or new observations which were 

 suggested by the collectors' notes and the evidently very rich material of the 

 Brussels herbarium. In several cases amended and extended descriptions are 

 given, without, however, adding much that is new. Not less than ten pages 

 are devoted to Landolphia owariensis, which would appear to be extremely 

 polymorphic, unless indeed the author included several distinct species under 

 that name. As in his Mission Laurent, Dr. De Wildeman pronounces himselt 

 also here in favour of the cutting method against the tapping of the rubber vines ; 

 and here he is in accord with one of the most competent authorities on the 

 subject, namely Dr. Aug. Chevalier, who also thinks that the tapping is in 

 the end more destructive to the vines than their cutting back to some distance 

 above the base. The cumbrous synonymy of the three genera is dealt with in 

 three separate lists, which, like the table of vernaculars, should be very useful, 

 although the latter will have to be accepted with caution. 



Otto Stapf. 



