Mechanical Science, S^-c. 165 



observed at the centre of the rods. An archer's bow also affords 

 a neat temporary instrument for the measuring of weights, or 

 forces, by attaching them to the middle of the string and observing 

 the deflection of the cord from a straight line. — Tech. B.ep.\'\. 196. 



5. Improved Cowl. — An improvement on the common traversing 

 cowl for the top of chimneys was copied from a French frigate, by 

 Captain Warren, R.N., and found to answer on-board his ship 

 beyond expectation. It is conceived that it might be applied 

 with effect on shore, in situations where inconvenience is oc- 

 casioned by eddies or high winds. The contrivance is simply 

 inserting a tube, shaped like a speaking trumpet, and open at both 

 ends, into the back of the common cowl so that its wide extremity 

 should form, as it were, the back of the hood, and its narrow ex- 

 tremity terminate a few inches within the mouth. As the wind 

 blows at the cowl, this tube causes a strong jet of air to pass 

 through it, and is found materially to assist the draught of the 

 chimney. — Mech. Mag. 



6. Phenomena of Comets. — M. de Biela, an officer of grenadiers 

 and amateur astronomer at Prague, is said to have observed a 

 remarkable phenomenon in the comet which he first observed on 

 the 30th of December of last year. On the night between the 

 22d and 23d of .January, the comet, besides the tail on the side 

 opposite the sun, had another turned towards the sun. These 

 two tails were not exactly opposite to each other, but formed a 

 very obtuse angle. M. de Biela, who is certain that there was no 

 optical illusion either in the instrument or the eye of the observer, 

 thinks that the most probable explanation of the second tail is, 

 that the comet had left behind it a luminous track in its passage, 

 and that this second tail indicated the path which the comet had 

 just travelled. It was neither so brilliant or so long as the tail 

 opposite to the sun, and was observed only on the 22d, 25th, and 

 27th of January, neither before nor after. 



M. de Biela also conceives that he has observed an influence, 

 exerted by the proximity of comets on the luminous state of the 

 sun, and has traced the increase of spots on its surface as comets 

 have approached that luminary — Nciu Monthly Mag. 



7. Substitution of Potatoes for Soap. — M. Cadet de Vaux pro- 

 poses to wash linen by the application of potatoes only three parts 

 boiled instead of soap. The following is an experiment on this 

 subject, made by M. Hericart de Thury, the report of which signed 

 by him has been published. 



Thi' linen e.Nperimentod on consisted of the cloathes of adults 

 and children, sheets, coverlids, table-linen, towels, brewers' aprons, 

 hospital linen, 8fc. The whole was first thrown into a tub to soak 

 in water for about an hour ; it was next placed in a copper of hot 



