During two snowstorms my instrument in a room here showed 130 degrees more heat than it indicated two years ago during extreme cold; on plunging the instrument into snow it indicated 30 degrees less, therefore only 100, but immersed in snow and salt, it showed a further 100 degrees less, and I believe in reality it marked still less but the snow and salt prevented it being seen clearly. In the greatest heat of summer the instrument stood at 360 degrees, and hence it appears that snow and salt increase the cold about one-third of the difference between extreme heat of summer and extreme cold of winter, a remarkable fact the reason for which I cannot determine. I shall learn with pleasure your opinions, especially what you have observed of the cold produced by saltpetre, of which I have heard many things, but have not personally seen. It will be difficult to send the instrument direct to you; it would be easier, I think, to have one made there."
A month later (15 March), Sagredo wrote to Galileo: "I have daily altered and improved the instrument for measuring temperature; if I could speak with you in person I could tell you from the beginning the whole history of
