Dec. 19, 1878] 



NATURE 



149 





their repeated warnings, but little attention has hitherto 

 been given. We mean the composition of the charcoal. 

 According to the manner of preparing this, the method 

 adopted for charring and the material employed, so does 

 the chemical composition of the charcoal differ. Some 

 samples, for instance, prove on analysis to contain 85 per 

 cent, of carbon, while others have 20 per cent, less ; it is 

 scarcely to be expected that gunpowder made from the 

 two kinds will have the same burning qualities, and yet 

 with gunpowder manufactures charcoal is charcoal, no 

 matter how much its component parts of carbon, hydro- 

 gen, oxygen, and ash may differ. It is of Uttle use, there- 

 fore, paying any particular attention to the physical 

 qualities of gunpowder so long as its chemical compo- 

 sition is almost entirely ignored. 



The manner in which the strain upon the gun and the 

 velocity of the shot are measured at Woolwich are worthy 

 of explanation. The means employed are of the simplest 

 kind. The maximum pressure of the gases inside the gun 

 as the shot is being expelled is recorded by what is termed 

 a " crusher gauge." This is no more than a tiny pillar of 

 copper. The pillar is placed loosely in a tube, the end of 

 which, made of steel, stands firm and fast no matter 

 what the pressure. So that the soft copper pillar, 

 when subjected to the action of the gas, gets com- 

 pressed, or crushed, and assumes something of a barrel 

 shape. The pillar and its case, being affixed to the base 

 of the shot, gets the full pressure of the gunpowder 

 gases, and its length afterwards denotes how much this 

 pressure has been. To secure more trustworthy pillars 

 of the metal it is the practice to compress them first of 

 all to a certain degree, to remove any honeycornb or im- 

 . perfection, and, thus uniformly compressed, they may be 

 relied upon to record the strain with accuracy. Com- 

 parison of the fired piUar, with other pillars which have 

 been subjected to known pressures, at once reveals the 

 degree of force to which the former has been subjected in 

 the gun. The maximum pressure, or strain, to which the 

 80-ton gun should be subjected, is set down as 25 tons on 

 the square inch, and it is with the aid of this " crusher- 

 gauge ' ' that the strain exerted in the various experiments 

 has been ascertained. 



The initial velocity of a shot, or, in other words, the 

 rapidity with which a projectile flies at the outset of its 

 career, is now measured by an electrical instrument, the 

 invention of Major le Boulengd, a Belgian officer. As 

 in the case of other instruments of a like nature, the shot 

 is made to break through two wire screens, placed at some 

 distance from one another. The intenal is usually about 

 100 feet. The screen is simply a wooden framework with 

 fine wires zigzagging across, and it is these fine wires 

 which the shot cuts. One screen is near the muzzle of 

 the gun, and the other at the distance we have men- 

 tioned. No. I screen is in connection with "an electro- 

 magnet in the instrument-house, and No. 2 screen with a 

 second, the two magnets hanging close together. While 

 the wires in front of the screen are perfect, an electric 

 current passes without interruption, and the electro-mag- 

 nets in connection with them are endowed with power, 

 but this power ceases as soon as the shot cuts the wires 

 of the screen. Before the gun is fired there is suspended 

 to the magnets two rods of iron, which remain, however, 

 only so long as the magnets are magnets. When the 

 shot is fired. No. i screen is torn, and down falls the rod 

 suspended to No. i magnet ; an instant afterwards, when 

 the shot has reached No. 2 screen, No. 2 magnet also 

 loses it virtue, and down falls the second rod. The time 

 between the falling of the two rods is so small, that ere 

 the first has fallen half its length the second has dropped 

 upon a trigger, which trigger darts out and strikes the 

 side of No. I rod. When the latter is picked up, the 

 first thing is to examine the surface for the mark of the 

 trigger, for the position of this mark, whether high or 

 low, tells ihe operator what he wants to know. The red 



\J 



being of a given weight, always takes the same tima to 

 fall, and according whether it has fallen half or quarter 

 its length, so the time taken by the shot to travel between 

 the screens has been long or short. In a word, the rod 

 has only to be compared with a prepared scale in order 

 to read off the number of feet per second at which the 

 shot has gone on its way. 



THE REGISTRARSHIP OF LONDON UNI- 

 VERSITY 



AST week we referred to Dr. Carpenter's intended 

 resignation of the Registrarship of the University 

 of London. We have before us his letter intimating hft 

 desire to resign his post on May 31 next, and the resolu- 

 tion of the Senate in connection therewith. By the date 

 mentioned Dr. Carpenter will have completed his twenty- 

 third year as Registrar, and, including his previous nine 

 years as Examiner, his connection with the University' 

 has extended over four-fifths of its term of existence, and 

 over a corresponding proportion of his own professional 

 life. There is no doubt that the success of this great 

 institution is to a great extent owing to the energy and 

 faithfulness with which Dr. Carpenter has discharged the 

 duties of his post. It has been fortunate for the University 

 I as well as for science that a man of so eminent a 

 j scientific position has been so long and so intimately 

 I connected with it, and it will be extremely difficult to find 

 i one capable of taking up adequately Dr. Carpaiter's 

 work. We have pleasure in publishing the resolution of 

 I the Senate, to which we have referred. 

 i " In accepting the Registrar's resignation of the im- 

 portant office he has held since 1856, the Senate desire 

 to record their sense not only of the abiUt)*, judgment, 

 and fidelity with which he has uniformly discharged its 

 duties, but also of the zeal and efficiency with which he 

 has on all occasions exerted himself both within and 

 beyond the limits of his official obligation, for the pro- 

 motion of the best interests of the University. 



" The Senate would further record their conviction 

 that it has been of special advantage to the University, 

 during the twenty years of its most rapid development, 

 to have had the services of a Registrar who, besides 

 being an excellent administrator of its affairs, has 

 attained, by his scientific labours, a position which has 

 given him a just weight and influence over those with 

 whom he has been brought officially into contact. 



" The Senate strongly recommend the Registrar to the 

 favourable consideration of the Lords of Her Majestj-'s 

 Treasury as having acquired, by 'special services,* a 

 claim to a larger superannuation allowance than that to 

 which he is entitled by mere length of serxnce." 



I 



ABOUT FISHES' HEADS 



N a former number (voL x\'ii., p. 286), in a note "About 

 Fishes' Tails," we called attention to some recent 

 observations of Alexander Agassiz on the young stages of 

 some fishes, in which he showed the wonderful changes 

 that, as development went on, took place in their caudal 

 I fins ; yet strange though these changes are, they seem as 

 nothing to those that take place in some fishes' heads, 

 and the facts first noticed by Steenstrup, and the theory 

 which, by a marvellous power of intuition, he built up 

 thereon, as to the eye in a flounder passmg from the right 

 side of its head to its left, have been in a great measure 

 confirmed, and perhaps in a greater measure added to, by 

 the painstaking observations quite recently published, of 

 .\lexander Agassi z,i firom which it would now seem very 

 certain that even the most shapeless adult fishes begin 

 their life as quite symmetrical young creatures. No more 



.•»' ProcerdiHgtof the American Academy <rf Arts and SdenceSi ^ot'«rr«»» 



July, 1878. , ... V . .. ., .. ... ..".; -JlZ^^f 



