USEFUL PROJECTS. 



ooo 



ciftit length of time, and to count 

 these vibrations, machinery and a 

 power are necessary, which may 

 exert a small but constant effort to 

 renew the waste ot motion j and 

 the difficulty is, so to apply these 

 as that they shall neither retard 

 nor accelerate the vibrations. 



In order to avoid the uncertain- 

 ties which respect the centre of os- 

 cillation, I have substituted an uni- 

 form cylindrical rod, without a bob, 

 for the pendulum. 



Could the diameter of such a rod 

 be infinitely small, the centre of os- 

 cillation would be exactly at two 

 tiiirds of the whole length, mea- 

 sured from the point of suspension. 

 Giving it a diameter which shall 

 render it sufficiently inflexible, the 

 centre will be displaced indeed, 

 but, in a second rod, not the 

 (1)600,000 part of its length, and 

 not the himdredth part so much as 

 in a second pendulum with a bob. 

 This displacement is so infinitely 

 minute then, that we may consider 

 the centre of oscillation, for all 

 practical purposes, as residing at 

 two-thirds of the length from the 

 point of suspension. The distance 

 between these two centres might 

 h't easily and accurately ascertained 

 in practice. 



But the whole rod is better for a 

 standard than any portion of it, be- 

 cause sensibly defined at both its 

 extremities. 



The uncertainty arising from the 

 difference of kngth requisite for the 

 second pendulum or rod, in different 

 latitudes, may be avoided by fixing 

 on some one latitude, to which our 

 •tandard shall rcfc r. 



To give an uniform impulse to 

 the rod, to renew the waste of mo- 

 tion occasioned by the friction and 

 te';istance of the air, I have made 



an improvement on the escapement 

 of the common clock, which effec- 

 tually prevents any irregularity, that 

 might otherwise be occasioned by 

 the unequal action of the wheels. 



To make the experiment, nothing' 

 more is necessary than such a clock, 

 and a piece of straight iron wirej 

 of about the diameter of a common 

 goose-quill ; and the length that 

 will be found to nbrate seconds, 

 will be about fifty-eight English in- 

 ches, from the point of suspension 

 to the end of the rod. The most 

 certain way of proceeding in tnc 

 experiment is, to have the rod at 

 first too long, and to continue cut- 

 ting small portions off thelower end, 

 till the clock is brought to time. 



The advantage that the above has 

 over all other pendulums, for ascer- 

 taining an universal standard of 

 measure, are, 



First, that it cati be regulated 

 with more certainty. 



Secondly, that it is one-third 

 longer, and therefore can be divided 

 with more certainty. 



And> thirdly, its simplicity, whicTi 

 puts it in the power of any person 

 to make the experiment with the 

 greatest accuracy, even without the 

 use of figures ; tlie whole (after 

 the clock is regulated) being ascer- 

 tained by one single measurement 

 of a straight line. 



A method of preparing a sulphw 

 reous viedkinaL ivater, by the re- 

 vererid Edward Kermcy. From 

 the Irish Transactions. 



CHEMISTS differ in opinion 

 concerning the process of na- 

 ture in the formation of sulphureous 

 waters. Whilst all agree, that sul- 

 phur by itsslf is not soluble in wa- 

 A a 2 ter, 



