444 



NA TURE 



{Sept. 5, 1889 



carrying arm of the remontoire is attached a small chain 

 or wire, which communicates any motion it may have to 

 the lever, L, from the other end of which lever hangs a 

 weight, w, smaller than W, which weight is therefore 

 raised when the re77totitoire arm is lowered, and lowered 

 when the remontoire arm is raised ; Q is a disk of metal 



Fig. 3. 



on a vertical spindle of a uniform motion clock, and 

 revolving rapidly (say 300 per minute). When the weight, 

 w, is below its mean position, it is in contact with the disk 

 Q, and (the lower end of it being coated with leather) 

 produces a considerable amount of friction, and therefore 

 tends to retard the speed of the clock ; when the weight, w. 



Fig. 4. 



is above its mean position, it is altogether out of contact 

 with the disk Q. The action is as follows : Supposing 

 the shaft. A, to be revolving exactly one per minute, the 

 pendulum to be vibrating exactly 60 per minute, and that 

 there are 30 teeth in the scape-wheel, it is evident that the 

 remontoire arm, and therefore, the weights, w and w, will 



vibrate backwards and forwards the same distance each 

 second, and that the mean position of all will be the same 

 each second. Under these circumstances, the weight, w, 

 will be alternately 0-5 second in contact with the disk Q, 

 and o'5 second out of contact, and the uniform motion 

 clock is rated, per se, just so much fast, that the resting 

 of the weight, w, for o"5 second in each second, will bring 

 the rate right. 



Now, suppose an error of acceleration to arise in the uni- 

 form motion clock, the mean position of remo7itoire arm 

 will rise ; therefore w will fall, and, instead of rubbing in 

 contact with Q for o"5 second, it will rub for 06 or 07 

 second, according to the extent of the error. This will 

 tend to check the rate, and this check will continue till the 

 relative position of the uniform motion shaft becomes as 

 it was when the clock was going correctly. 



If a retardation occurs, the reverse effect will take place, 

 and the weight, w, will rub only for o'\ or 0*3 second, 

 instead of o'5, until the error be corrected. 



So far as described, there was no particular novelty, as 

 most of this arrangement, in principle, had been tried be- 

 fore, the failure that had resulted being due to the fact that 

 it was found impossible to prevent the pendulum being 

 influenced by the difference of force on the pallets, 

 under varying circumstances, the pendulum being in the 

 former case driven by the scapement ; not by electricity, 

 as in this case. 



This difficulty was got rid of by :— 



(i) Making the pallets (as they are not required to 

 drive the pendulum) of such form that the teeth of the 

 scape-wheel impinge upon them nearly at the angle of 

 repose. 



(2) By driving the pendulum by electric current from 

 another clock, thus virtually rendering the pendulum not 

 a pendulum at all, but a lever worked backward and for- 

 ward by electricity, and not subject to alteration in its rate 

 by slightly varying force on the pallets. 



An arrangement is also attached (but not shown in the 

 figure, to avoid confusion) by which, if either portion of the 

 clock fails to do its duty from want of winding, want of 

 electric current, or other cause, the connection between 

 the two systems is instantly severed, automatically. 



( To be cofttinued.) 



NOTES. 



Mr. Griesbach, of the Geological Survey of India, who has 

 lately been engaged in geological woi-k in Afghanistan, and who 

 was geologist to the Afghan Boundary Commission, has been 

 appointed to Beloochistan, " to carry on geological investigations 

 into the mineral deposits of the country." 



At the meeting of the British Association at Newcastle there 

 will be a joint discussion by Sections B and G of a paper to be 

 read in the latter Section by Sir I. Lowthian Bell, F. R.S., 

 President of Section B, on "Blast Furnace Practice." 



The International Astronomical Congress will hold its sittings 

 in Brussels from the loth to the 12th inst., and at Liege on the 

 13th. The attendance from all European countries and America 

 will, it is anticipated, be very large. 



It is reported from Brussels that M. Dutoit, the Transvaal 

 Minister of Public Instruction, is now endeavouring in Belgium 

 and Holland to recruit the necessary staff for organizing a Dutch 

 University in Pretoria, the capital of the Transvaal. 



Colonel Thuillier's report on the progress of the Survey 

 of India for the past year shows that the party employed on the 

 trigonometrical surveys has completed the 370 miles remaining 

 of the secondary triangulation along the east coas' o"^ India. 

 The secondary triangulation was also carried out for an aggregate 



