To Rudolf Clausius   27th Nov. 1858

London 27^th Nov. 1858

My dear Clausius

Many times since my return to England has the thought of writing to you occurred to me. I wished among other things to tell you the great pleasure which my short visit to Zürich¹ gave me, and how gladly I would have returned there in accordance with your kind information if my engagements had permitted me. After parting with you upon the Lauzplatz² we³ made the best of our way to Rosenlaui,⁴ and spent a morning upon the glacier. Here a Frenchman deliberately stole my boots; he was followed, overtaken on the Sheideck⁵ where they were taken off his feet. He had left me a miserable old pair in their place. We stayed two days at Grindelwald, and examined both the glaciers.⁶ Then we crossed the Strahleck⁷ to the Grimsel;⁸ visited the Rhone glacier⁹ and afterward went down the valley to Viesch.¹⁰ We ascended the Eggishorn,¹¹ and remained at the hotel there 8 days. During this time I examined most of that grand Aletsch glacier,¹² from its source downwards, and finding a hardy guide¹³ at the hotel he and I ascended to the summit of the Finsteraarhorn.¹⁴

We afterwards went to Zermatt,¹⁵ where my friend Ramsay¹⁶ receiving intelligence of the death of his mother, left me and returned to England. I had a guide¹⁷ from Lauterbrunnen,¹⁸ a strong fellow & good glacier man, he had never been up Monte Rosa,¹⁹ but I thought as both of us were good climbers we might try it together. We did so on the day after our arrival at the Riffel²⁰ and succeeded in reaching the top. We saw nothing: for hours we toiled amid impenetrable gloom, dark, dense clouds and falling snow. I made a few observations on the top, but the most wonderful thing I have ever seen was the form of the snow crystals. There was not a breath of air stirring to injure them, and they descended as a shower of frozen flowers. Each flower had 6 leaves: there were endless variations, but no deviation from the 6 leaved type. any thing so beautiful I had never before seen. But what will interest you most was the following observation. In the earlier portion of the day we had sunshine, and not until we came near the summit did the snow begin to fall, though we were enveloped in clouds long before. I tried the colour of the snow as we ascended, driving the Alpenstock²¹ into it, but the blue was hardly perceptible. On coming down however after a thick layer of fresh snow had fallen the colour was magnificent, on drawing the Alpenstock from the snow, a most exquisite blue would fill the hole made by the stock, and as my guide walked in front of me, where he lifted his feet, and shook the snow from them, gleams of blue light seemed to flash from it. At this time the darkness was so great that we could not see more than 20 yards in any direction—there was not a trace of the blue heaven to be seen, and this observation agrees with all that I made before and since, that this exquisite blue color is a property of the newly fallen, and finely granular snow. A week afterwards the weather was magnificent. One glorious day I had lent my guide to a party of gentlemen; so wishing to take advantage of the weather I started in my shirt sleeves, carrying with me about three ounces of food, and half a pint of cold tea, and without wine, or brandy, coat, or guide, I climbed to the Höchste Spitze²² of Monte Rosa.

I had often seen interference colours on the clouds, but had never observed any thing to equal the magnificence of those I saw during this second ascent of Monte Rosa. The day was glorious, and generally without a trace of vapour. Three times however during my ascent a light veil of cloud drew itself across the sun, and at each time the veil was flooded with the most gorgeous colours. Red, orange, green, yellow, blue—all nearly as vivid as the hues of the spectrum. This was by transmission—but I have seen similar colours by reflective light among the clouds. They must be excessively thin, and I think the colours must be those of mixed plates—do you not think so?

I waited 11 days at the Riffel, and explored the whole system of glaciers from the Cima de Jazzi²³ to the Zmutt glacier.²⁴ My main object in going to Switzerland was to learn something more about the structure of the ice. M^r. Mousson²⁵ (to whom I beg of you to remember me most kindly) was quite right in regarding the question unsolved. I had a strong opinion on the subject it is true, but as your friend Herr Moleschott²⁶ says it is easy to have opinions—but I wanted proofs. These proofs I am happy to say I obtained this year, and I think I shall be able to establish a perfect parallel between the structure of glacier ice & the cleavage of rocks.²⁷

I passed from the Riffel to the Allalein glacier,²⁸ then to the Fee gl.²⁹ in company with our friend Hirst, who was on his way over the Moro³⁰ to Rome. Afterwards to Chamouni³¹—I met Magnus³² & his family on the slope of the Montanvert,³³ and also saw Ettingshausen.³⁴ I reached the top of Mont Blanc³⁵ a second time & planted a thermometer there. This was the end of my Campaign—I wish you would give me your opinion about the snow & the clouds. When you see the professors Fick³⁶ remember me kindly to them—Believe me dear Clausius

Ever most sincerely yours | John Tyndall

I wish you a happy Christmas.

RI MS JT/1/T/175