Letter from John Dalton to Peter Crosthwaite

Kendal 6 mo 21st 1788


Esteemed friend,

Inclosed is a copy of my journal for the last half year- The substance of it needs no further explanation; but I have lately added a fresh column relative to the Tides of the Air; these will happen about the same time each day as the Tides of the ocean, that is about three hours after the Moon has cross’d the meridian: I get the Moon’s Southing each day from the Gent. Diary, and adding 3 hours thereto, gives the time of High Air (if I may be allowed to call it so) and then dividing the times for any 2 Days gives the Time of the intermediate Tide; these I set down each day to be a quarter of an Hour (rejecting odd minutes) in a separate column. – What gave rise to this was a supposition that these Tides may possibly give birth to some of the more minute changes in the Weather, or that they may have some influence on the Aurora Borealis, a Phenomenon, which has baffled the Sagacity of the last and present age to account for in a satisfactory Manner. The Times of the 4 Quarters of the Moon are also set down; together with the Times when the Moon is in Perigee or Apagee, or nearest to, and farthest from the Earth, in each of its Revolutions; as the Tides are higher, the nearer the Moon is to the Earth, Other Circumstances being the same – since this commenced I have been more particular to the Time of Day when any change occurred.

Should have been glad to have been glad to have embraced this opportunity to send a Thermometer; but am totally disappointed. The Glassmen either despair of pleasing me or are unwilling to trouble themselves with such trifling matters. The Tradesman in this Town I employed has received his order in full, but there is no mention made of mine. However, I intend to apply somewhere else.- The spirit Therm.r which I suppose thou hast yet, might serve my purpose, if it had a Fahrenheit scale, for 6 or perhaps 12 months without much error. A scale from 0 to 100 might be had by determining any two different Degrees by means of Water of different Degrees of Heat and the other Thermometer. The principal Objection is the too large Bulb.

From what thou hast mentioned of the Barometer, I think it is now high as it can be got, and very near the truth. Thy Brothers must be 1 or 2 sixteenths too high for your Elevation, I think; and this may arise from 2 Causes, either an Adulteration of the Silver, or a wrong Measurement from the Bason; or perhaps both together. The real Difference is Height of our Barometers will be found best by comparing the monthly means of the same (which in my Journal I put down in Inches and Decimals at the End of Each Month). I suspect that this Difference will give a greater Difference of Elevation of the Two places than otherwise we make it: My Barometer will be about 20 Yards above the sea; and if thine be 55, the Difference 35 will scarce give 2/16 of the Barometer. And yet there is great Reason to believe Thy Barometer is as true as mine since I filled it afresh: This leads me to mention a late Circumstance. A Friend of mine from Cumberland being here mentioned his having seen (he thinks in Manuscript at the End of Dr Johnson’s Tour to the Hebrides) that Skiddow was 1148 yards above the Sea and that Grassmere Top was 1145 yards above the sea; Upon this I told him that Donald had made Skiddow 1090 yards above the sea, and that it was supposed the foot of Bassenthwaite was about 40 years above it. But with this last supposition he said he could not coincide for it only supposed the River about 4 Yards fall for 1 Mile, which he was persuaded was much too little, and alleged that he knew several Mills upon it where the Dam was 1 ½ or 2 Yards above the river below and the dead Water in the Dam was only two or three Hundred Yards; add to this that the Mills are generally built on a Part of the River where is the least fall: also that he knew the River in general to have a pretty rapid stream.- Now from these Considerations it would seem that the Foot of Bassenthwaite should be set at above 40 yards above the Sea. So that it will not appear surprising if our Barometers should differ more than 2/16ths.

Please to give me a word relative to the situation of thy Thermometer: mine hangs out in the open Air in the Garden this fair Weather at Morn and Night; but is under cover at Noon and is often I believe too Hot for it is to the South and the Roof heated by the Sun in clear Days. Different situations make sensible Variations in them: J Gough and I mostly agree at Morn and Night; but the Noon observations differ, especially in clear days sometimes 5 or 6 Degrees: However our Monthly Means come mostly within one or two Degrees, and often are not one different.

I do not think thou will lose any Thing sensible from thy Bottle by Evaporation; but can perhaps speak more decisively on this Head hereafter being at present partly engaged on Experiments of this Nature. It appears from the public Papers, that you have had a respectable Number of Visitors to the Lakes this year already – I hope their Curiosity would be no less gratified by a sign of the Museum than by the Beauties of Nature in your Vicinity.

If Business have hindered thee from completing thy copy, do not hurry on our Account.

With best Respects, thy Friend

John Dalton