236 Intelligence and Miscellaneous Articles. 



what constitutes a good creosote oil, and would exclude oils of the 

 highest preservative Character. "We have lately examined timber 

 " pickled '* 3') years ago with creosote oils from the London tar, 

 and which oils "when cooled to 40° E. yielded a very large amount of 

 naphthalene: and vet the wood remains perfectly sound to this day. 



The directions for the preparation and estimation of pure phenol 

 (carbolic acid) are very minute, and include the results of the most 

 recent workers on the subject. The author also describes the 

 methods of preparing carbolic soap and disinfecting powders. 



The chapter on Ammouiacal Liquor is well written, and contains 

 a full account of all the substances contained in it ; directions are 

 also given for estimating its value, and for working it up. This 

 latter part of the work is fully illustrated with engravings. 



In conclusion, we congratulate the author upon having produced 

 a work which is absolutely indispensable to all manufacturers of coal- 

 tar products. 



IVorl-ed Examination Questions in Plane Geometrical Drawing. 

 By E. E. Hul^ie. Longmans, Green, and Co. : London. 

 This work consists of three hundred questions taken from old 

 examination papers, two thirds of which have figures correspond- 

 ing to them, said to be solutions of the problems. There is no attempt 

 at classification ; on the contrary, it has been purposely avoided by 

 the author, and for a reason with which we do not hold. There 

 are no demonstrations, and in most cases only scant directions ; and 

 even these are given where least, and omitted where most, needed. 

 Many of the constructions are empirical, and incapable of being 

 demonstrated ; hence, from a mathematical point of view, they are 

 not solutions at all. Scale Questions, those bugbears of Candidates 

 for Military Examinations, ought to have been collected, and com- 

 plete solutions of typical cases given. What good results from 

 answering precisely similar questions over and over again ? Not- 

 withstanding its many defects, there is much in the book to re- 

 commend it. The questions are such as are certain to be encoun- 

 tered in Woolwich and Sandhurst papers ; and the constructions 

 are well drawn and conveniently placed for easy reference. 



XXVIII. Intelligence and Miscellaneous Articles. 



ON THE DURATION OF THE PERCEPTION OF LIGHT IN DIRECT 

 AND INDIRECT VISION. BY AUG. CHARPENTIER. 



A FTEE various experimenters, I have sought to determine the 

 time that elapses between the appearance of a light before the 

 eye and the making of a signal by the subject of the experiment as 

 soon as he perceives the light. There was interest in ascertaining if 

 the duration of the perception was different for the centre and for 

 the excentric portions of the retina, if exercise could modify that 

 duration, and if the modification would or would not be limited to 

 the part exercised. 



Eor these experiments the eye, place at the centre of a Landolt's 

 perimeter, looked into a large box lined with black, in the bottom 

 of which a perforation had been made, about 1 square centim. in 



