HARJDWICKE'S SC lENCE-GOSSIF. 



227 



Hoffmann, a Baerjer, a Kolbe, &c. More and more 

 difficult problems are placed in his hands, and the 

 assistance of the professor is gradually withdrawn 

 till he feels himself fully capable of original research, 

 whether in speculative or applied chemistry. It is 

 the interest of the professor to detect, train, and 

 bring out ability. The researches and discoveries 

 made in his class are his 'results.' The more 

 numerous and important such researches, the more 

 students flock to his laboratory and his lectures. Rival 

 universities contend for his service, and Government 

 awards him public honours." 



Here we see a community of interest between the 

 professor and the student. Not so with our examiners 

 and their victims. The examiner, who is paid on the 

 piecework priniciple, so much per gross of papers 

 excrmined, is interested in the non-success of the 

 •candidate. If "plucked" he comes up again, pays 

 another fee, contributes another paper, and thus 

 improves the examiner's income. If he is passed, 

 the examiner gets no more out of him. The drudgery 

 of toiling through a multitude of examination papers 

 is so irksome that nobody undertakes it for any other 

 than mere pot-boiling motives, excepting in the case 

 where the teacher examines his own pupils for the 

 legitimate and necessary purpose of determining his 

 progress, and for filling up the gaps of knowledge 

 revealed by the examination. When I was a student 

 in Edinburgh the only examiners were the professors ; 

 the ablest of these had weekly or monthly class 

 examinations, and kept a record of the status of each 

 student, so that the formal examination for his 

 degree was only one of a series. In such cases the 

 grinder could do nothing more than assist the student 

 in the legitimate recapitulation of the work he had 

 already gone over. The professor himself should be 

 a trustworthy man and a teacher. The only use of 

 outside examiners in such cases is the examination of 

 outside students, those who may have acquired the 

 requisite amount of knowledge without entering the 

 university classes. Such examiners should receive a 

 fixed salary or honorarium, not be paid by piecework, 

 and all examinations should be both written and oral. 

 By cross-questioning on the answers given on a 

 written paper, mere verbal cramming may easily be 

 detected. 



An experiment recently made on feeding the 

 horses of the 7th Cuirassiers with a mixture of oats 

 and cocoanut meal, is worthy of the attention of our 

 commissariat officers who are on duty in the tropics. 

 We are told that the condition of the horses was 

 much improved, and that the reduction in the cost of 

 horse-keep amounted to 50 francs per annum. 



On the 6th of November, 1883, the marble memorial 

 statue of Liebig erected at Munich was found to be 

 covered with a number of black spots and stripes. 

 These were examined by Pettenkoffer, Baeyer, and 

 Zimmermann. The stains were found to consist of a 

 .mixture of silver with a little hydrated manganese 



dioxide, from which it is inferred that the liquid used 

 by the contemptible defiler was a solution of silve 

 nitrate and potassium permanganate. The stains have 

 been removed by converting the metals into sulphides, 

 and tlicn dissolving these sulphides with potassium 

 cyanide. A paste was made by moistening porcelain 

 clay with ammonium sulphide. This was laid over 

 the stained surface and renewed after twenty-four 

 hours. After the lapse of another day it was carefully 

 washed off. The silver and manganese compounds 

 were thus converted into sulphides, and still black. 

 Two applications of a paste of porcelain clay moistened 

 with a saturated solution of potassium cyanide, re- 

 stored the marble to its original whiteness. 



CHAPTERS ON FOSSIL SHARKS AND 

 RAYS. 



]5y Arthur Smith Woodward. 



11. 



AS the genera of sharks belonging to the first four 

 families possess no dorsal spines, they are only 

 represented in the fossil state by teeth, vertebral 

 centra, and shagreen. They are all very rare in 

 strata earlier than the Cretaceous, and do not appear 

 to have flourished in considerable numljers until the 

 old Hybodonts and Cestraciontoid sharks were on the 

 verge of extinction. 



Carchariid^. 



The earliest fossils that can be definitely referred to 

 this family are the teeth included by Agassiz in his 

 genus, Corax. Two species occur abundantly in the 

 English Chalk, and the smallest of these {C. falcatiis) 

 has also been met with lower in the Cretaceous series 

 in the rocks of the Continent. The teeth, which are 

 triangular in shape, with regularly serrated edges, are 

 solid throughout, having no internal cavity ; and in 

 external form they agree so closely with the dentition 

 of the living Carcharias, that some pakieontologist 

 are inclined to believe in their generic identity. Fig. 

 134 represents a tooth of C. falcatus* and fig. 132, 

 one of the larger species, C. pristodontiis. In the 

 latter, it will lie observed, the root is relatively much 

 larger than in the former, and the edges of the crown 

 describe curious curves that are characteristic and 

 unmistakeable. The existing genus, Galcocerdo, 

 seems to replace Corax in the Tertiary formations. 

 The teeth of this shark are also serrated on the edges 

 of the cone, but not quite to the summit, and the 

 denticulations are irregular, those at the basal portion 

 being much less pronounced than those somewhat 

 higher. Only one species of Galeocei'do has been 



* Some of the smaller teeth referred to this species are desti- 

 tute of serrations on the edges ; such may possibly have belonged 

 to young individuals, for it is known that the dentition oi the 

 young Carcharias consists of teeth without serrated margins. 



