VOL. XLI.] PHILOSOPHICAL TRANSACTIONS. 44/ 



is SO strongly illunnnated, that it may be examined with all imaginable ease and 

 pleasure. A convenient apparatus of this kind, with 4 different specula, and 

 magnifiers of different powers, has lately been brought to perfection by 

 Mr. Cuff. 



M. Leuwenhoek. says, (in his 2d vol. part ii. p. 93,) that sometimes, to 

 throw a greater light on his objects, he used a small convex metal speculum ; 

 and it is highly probable, that our double reflecting microscope may be owing 

 to this hint. Also, in the 4th volume of his works, p. 182, after describing 

 his apparatus for viewing eels in glass tubes, M. Leuwenhoek adds, that he 

 had another instrument, to which he screwed a microscope set in brass ; on 

 which microscope, he says, he fastened a little dish, that his eye might be 

 assisted to see objects better ; for he says, he had filed the brass which was 

 round his microscope, as bright as he could, that the light, while he was view- 

 ing objects, might be reflected from it as much as possible. This microscope, 

 with its dish, seems so like our opaque microscope with its silver speculum, that, 

 after considering his own words, it is probable he may properly be esteemed 

 the inventor of it. 



An Inquiry into the Causes of a dry and wet Summer. Anonymous. 



N°458, p. 519, 



This writer concludes, that a frosty winter produces a dry summer ; and a 

 mild winter a wet summer. And he finds, from these and some other observa- 

 tions, casually made, that the weather depends very much on the wind. He 

 therefore begins with inquiring what is the cause of winds, and then proceeds 

 to guess why the wind influences the weather. 



Wind is a stream of air ; air an unmixed fluid encompassing our globe, with 

 a shell of at least 60 miles thick. Every particle of air gravitates equally to- 

 wards the centre of the earth. Air is capable of being compressed and ex- 

 panded. The more air is compressed, the heavier it is; the more it is expanded, 

 the lighter. Cold and heat, whatever they be, or however they act, produce 

 these contrary effects in the air : that is, cold compresses the air, and heat 

 expands it ; therefore cold and heat, in different parts of the air, will make it 

 flow : for cold making the air heavy, and heat making it light, the lighter must 

 give way to the heavier ; as, in a balance, a greater weight makes a smaller rise. 

 We daily see a proof of this in a stove. 



The sea and land-breezes, and the trade-wind, owe their origin to these 

 causes. The sea-breeze, when regular, begins at 9 o'clock in the morning, 

 approaches the shore gently at first ; increases till 12; retains its full strengtii 

 till 3 ; then gradually decreases till 5, when it dies away. At 6 in the evening 



