750 



Pencoote of the East India House, under whose directions that ship 

 was fitted out : and it is to the great pains taken by Mr. Sims in 

 placing the magnets employed for counteracting the local attraction 

 that the author attributes the undeviating accuracy of those com- 

 passes during the whole time the Pluto was under his command in 

 both hemispheres. He observes that, in the first place, much care is 

 required in securing the magnets, and protecting them from wet, 

 after their proper position has been ascertained. In the case of the 

 Pluto, two magnets were placed under the deck in the author's cabin ; 

 one of them eighteen inches below the deck, being, it is true, an eye- 

 sore, but one of trifling consideration, when compared with the great 

 importance of the well- working of the compass. The next point to 

 be attended to is that the cards, or needles, should be all of the same 

 size, and exactly corresponding with that of the compass used at the 

 placing of the magnets for counteracting the local attraction. The 

 bittacies should all be of the same make and height, and the compass- 

 boxes of the same size ; so that whenever a new compass or a fresh 

 bittacle is wanted, the circle in which the needle moves may remain 

 at the same angle from the magnet as at the first adjustment. On 

 a strict attention to these precautions will depend the well-working 

 of the compass in all iron vessels, and also in wooden vessels when- 

 ever the quantity of iron they contain creates the necessity of mea- 

 sures being taken for counteracting local attraction. 



It has been alleged that the adjustments for local attraction made 

 in northern latitudes are not correct when the ship is south of the 

 equator ; but the author states that, in the Pluto, he observed no dif- 

 ference ; that ship having made, while under his command, passages 

 of many thousand miles, comprising 94 degrees of latitude, namely 

 from 51° North to 4'3° South, and 153 degrees of longitude, namely 

 from 30° West to 123° East, during the whole of which he never 

 found any other correction for the compasses necessary excepting that 

 required for the magnetic variation, the local attraction having been 

 completely neutralized. 



A diagram is subjoined, showing the positions of the compensating 

 magnets with relation to the compass. 



** Practical Remarks on Annealing Flint- Glass." By Apsley Pellat, 

 Esq., of the Falcon Glass Works, Holland Street. Communicated 

 by Joshua Field, Esq., F.R.S. 



This paper is entirely occupied with practical details relating to 

 the art of annealing flint-glass and depriving it of colour, the author 

 stating that he leaves the rationale of these facts to be explained by 

 philosophers. He thinks, however, that they are reconcileable with 

 the theory of Scheele, as explained by Bergman, and detailed by 

 Murray in his work on Chemistry. 



