700 I'HILOSOPHICAL TRANSACTIONS. [aNNO 1780. 



consumptive disorders, to the sea, or at least to places situated close to the sea, 

 which have no marshes in their neighbourhood. It seems also probable, that the 

 air will be found in general much purer far from the land than near the shore, 

 the former being never subject to be mixed with land air. 



It appears also, that the air in frosty weather is in general wholesomer than it 

 is in winter when it does not freeze ; and that uncommon warm weather, happen- 

 ing in the winter season, is apt to render the atmosphere very unwholesome : 

 the reason of which I apprehend to be, that the frost totally checks that general 

 tendency to corruption, which, being revived by warmth again, increases the in- 

 fection of the common air, which at that time is so much the greater, because 

 the plants, which are deprived of their leaves in winter, have no power in them 

 to counteract it. 



It seems also probable, that those countries which are, by their local situation, 

 exposed to noxious exhalations, are in general much wholesomer in the winter ; 

 and that it is much safer to cross such countries in summer time when it is 

 windy weather than in a calm, &c. Dr. Damman, an eminent physician and 

 professor royal in midwifery at Ghent, told me, that when he was formerly a 

 practitioner at Ostend, during 7 years, he found the people there remarkably 

 healthy ; that nothing was rarer there than to see a patient labouring under a 

 consumption or asthma, a malignant, putrid, or spotted fever ; that the disease 

 to which they are the most subject, is a regular intermittent fever in autumn, 

 when sudden transitions from hot to cold weather happen. — People are in general 

 very healthy at Gibraltar, though there are very few trees near that place ; which 

 is probably owing to the purity of the air, arising from the sea. Most small 

 islands are very healthy. At Malta people are little subject to diseases, and live 

 to a very advanced age. 



XXIP'. The Principal Properties of the Engine for Turning Ovals in IVood or 

 Metal, and of the Instrument for Drawing Ovals on Paper, demonstrated. 

 By the Rev. Mr. Ludlam, Vicar of Norton, near Leicester, p. 378. 

 The instrument for drawing ovals on paper or board is so common, that a par- 

 ticular description of it is needless. It is much in use among the joiners, and 

 called by them the trammels. One part of it consists of a cross with 2 grooves 

 at right angles : the other is a beam carrying 2 pins which slide in those grooves, 

 and also the describing pencil ; we shall distinguish these 2 parts by the names of 

 the cross and the beam. It is very well known, that all the engines for turning 

 ovals are constructed on the same principles with the trammels ; the only ditt'er- 

 ence is, that in the trammels the board is at rest, and the pencil moves upon it ; 

 in the turning engine, the tool, which supplies the place of the pencil, is at rest, 

 and the board moves against it. 



