From Hermann Knoblauch¹

Dear M^r Tyndall

I have hastened to get the crystals for our experiments and I send you a number of them.

1. Dioptas (from the ‘Kirgisensteppe’) rhomboëdric (like spar)

2. Diopsid

a) from the Mussa. Alp (Piemont)*

b) from Reichenstein.

cleavage parallel to the surfaces of the orig. prism.

*(fine green crystals, together with granates)

3. Eisenfreier Turmalin. (from Elba) rhomboëdr.

[3] cleavages (exactly the same with those in the common turmaline) converg. to the axis of the column.

4. Topas (from Saxony)

1 peace without iron (colourless)

1 " " " with " " " (yellow)

cleavage parallel to the ‘gerade Endfläche’)

5. Grauspiessglanz-Erz

1 cleavage parallel to the ‘gerade Endfläche’

an other " " " " ‘[Längesfläche]’.

to be compared with antimony in respect of the induction phenomena.

6. Sapphir

cleavage parallel to the ‘gerade Endfläche’.

7. Apatit

cleavage " " " " " " .

8. Wolfram

cleavage parallel to the surfaces of the original prism.

9. Grünbleierz

(2 peaces –) cleavage parallel to the ‘gerade Endfläche’.

same form with Apatit | Grünbleierz (Arsenikblei) contains ‘Kalkerde’ instead of lead.²

10. Petalit

cleavage parallel to the surfaces of the orig. prism.

11. Hornblende with iron

a) 2 little peaces

b) a large peace

12. Tremolit without iron

same crystalline form : (prismatic) to be compared.

13. Augit (from Bohemia). augit with iron.

same form as diopsid S. n^o 2. diopsid without iron.

14. Spinell

15. Automolith.

same octaïdric form, the one containing iron, the other not so.

16. Smaragd cleavage parallel to the ‘gerade Endfläche’.

Ewart ist leider nicht hier, so dass ich wegen der optischen Eigenschaften keine Auskunft erhalten kann. Ebenso ist du Bois verreist. Er hatte unsere Abhandlung noch nicht der Physikalischen Gesellschaft mitgetheilt. Ich that dies daher selbst in der Sitzung am vergangenen Freitag. Das Heft der Philosoph. Magaz., worin Ihr Aufsatz, ist bereits hier verbreitet. Poggendorff’s Februarheft, worin die deutsche Mittheilung, ist im Druck vollendet und erscheint in diesen Tagen.

Poggendorff ist hier der Einzige, welcher die Faraday-Plückerʼschen Untersuchungen näher kennt. Zu meiner Verwunderung sagte er mir, dass er eine Kupferscheibe, beim Öffnen der Kette immer angezogen gefunden hätte. (A copper disc attracted (by induction), when opening the circuit. As I remember, we found it repelled [2 words illegible]. Be so kind as to repeat the experiment before one pole with copper as well as with antimony and give me notice of the result). Plücker hat die Erscheinung beim Öffnen der Kette gar nicht bemerkt, Poggendorff konnte mir von der Gesammtheit der Wirkungen keine genügende Erklärung geben. Es wird daher gut sein, wenn wir unsern Plan ausführen, die Inductionserscheinungen im Zusammenhange gründlich zu untersuchen.

Einen Reostaten und eine Tangentenboussole habe ich bestellt, den ersteren in der Form, in welcher Prof. Poggendorff ihn bereits für wissenschaftliche Untersuchungen angewandt hat, die letztere, wie sie Prof. Dove anwendet. (Die Dimensionen der Tangentenboussole sind von denen der Bunsen’schen etwas verschieden, aber ich habe keinen Grund gehabt, sie abzuändern, da sie sich als zweckmässig erwiesen haben). Auf Ihren Wunsch theile ich Ihnen mit, dass der Reostat 19 Thaler, die Tangentenboussole 12 Thal. kostet. Ich denke auch noch einige andere Apparate mitzubringen.

Der Vollständigkeit wegen bemerke ich, dass Pinit nicht zu haben war. Lepidolith kommt nicht krystallisiert vor. – Rubellit ist eine Art Turmalin. Zircon ist unbrauchbar für unsern Zweck. Corund haben Sie im Sapphir. – Antimon und Arsenik-Krystalle giebt es nicht in geeigneter Grösse. Ebenso [wenig] Kupferkrystalle.

Plücker soll 2 Arten von Topas haben, wovon er den einen für [negativ], den andern für positiv hält. In Venedig beschäftigt man sich jetzt ebenfalls mit magnetisch-diamagnetischen Untersuchungen, wie ich aus einer Abhandlung ersehe, die mir so eben von Zantedeschi als Geschenk übersandt wird.

Es würde mir sehr erfreulich sein, wenn Sie die Güte hätten, mich zu benachrichtigen, ob die Mineralien richtig angekommen sind, und welche Resultate Sie [damit] erhalten.

Ich bin gern bereit, Ihnen sonst noch zu besorgen oder Ihnen Auskunft zu ertheilen, so weit dies irgend möglich ist. Ich bitte mir nur Ihre Wünsche baldmöglichst mitzutheilen.

Meine Wirthsleute (Gutmann) bitte ich zu grüssen und Ihnen zu sagen, dass Herr Krämer, an den Sie mir einen Brief mitgegeben hatten, vor einigen Wochen gestorben ist, weshalb ich den Brief nur seiner Frau übergeben konnte.

Mit den besten Grüssen an Sie und meine sonstigen Freunde in Marburg,

ganz der Ihrige

Herm. Knoblauch.

I join 2 [1 word illegible] crystals:

• Heulandit (from Fassathal) (red, containing iron)

• " " (from Island) (white, without iron).

cleavage parallel to the ‘schiefe Endfläche’.

_______

It appears to me of a peculiar interest to compare with each other

1) antimony and Grauspiessglanzerz.

2) arsenik-blei and apatit.

3) hornblende " tremolit.

4) augit " diopsid

5) spinell " automolit

6) 2 sorts of Heulandit.

they have [resp.] the same crystalline form (same cleavages) but different chemical constitution. Don’t confound the diff. crystals and keep them until I return; because I wish to see the experiments.

The lectures at the Berlin university are not closed before the end of this week. – My father, who regrets that you have not accompanied me, sends you his best compliments. After the close of the lectures you would have no profit here (as I believe), especially I am afraid you would have no opportunity of working in a laboratory.

RI MS JT/1/K/27

Dear M^r Tyndall

I have hastened to get the crystals for our experiments and I send you a number of them.

1. Dioptase (from the ‘Kirghiz Steppe’) rhombohedric (like spar)

2. Diopside

a) from the Mussa. Alp (Piedmont)*

b) from Reichenstein.

cleavages parallel to the surfaces of the orig. prism.

*(fine green crystals, together with garnets)

3. Iron-free Tourmaline. (from Elba) rhombohedr.

[3] cleavages (exactly the same as those in the common tourmaline) converg. to the axis of the column.

4. Topaz (from Saxony)

1 peace without iron (colourless)

1 " " " with " " " (yellow)

cleavage parallel to the ‘vertical face’)

5. Stibnite ore

1 cleavage parallel to the ‘vertical face’

another " " " " ‘longitudinal face’.

to be compared with antimony in respect of the induction phenomena.³

6. Sapphire

cleavage parallel to the ‘vertical face’.

7. Apatite

cleavage " " " " " " .

8. Wolfram

cleavage parallel to the surfaces of the original prism.

9. Pyromorphite

(2 peaces –) cleavage parallel to the ‘vertical face’.

same form as apatite | pyromorphite (arsenic of lead) contains ‘calcium oxide’ instead of lead.⁴

10. Petalite

cleavage parallel to the surfaces of the orig. prism.

11. Hornblende with iron

a) 2 little peaces

b) a large peace

12. Tremolite without iron

same crystalline form : (prismatic) to be compared.⁵

13. Augite (from Bohemia). augite with iron.

same form as diopside S. no. 2. diopside without iron.

14. Spinel

15. Gahnite.

same octahedric form, the one containing iron, the other not so.

16. Emerald cleavage parallel to the ‘vertical face’.

Ewart⁶ unfortunately is not here, with the result that I cannot obtain any information about the optical properties. Du Bois is away too. He had still not communicated our paper to the Physikalische Gesellschaft. I therefore did this myself at the session last Friday.⁷ The issue of the Philosoph. Magaz. in which your essay appeared has already been circulated here.⁸ Poggendorff’s February issue in which the communication in German⁹ appeared, has been printed and will appear in the next few days.

Poggendorff is the only person here who knows the investigations of Faraday and Plücker in more detail. To my surprise he told me that he had always found ‘a copper disc attracted (by induction) when opening the circuit. As I remember, we found it repelled [2 words illegible]. Be so kind as to repeat the experiment before one pole with copper as well as with antimony and give me notice of the result’). Plücker had not noticed the phenomenon at all when opening the circuit. Poggendorff could not give me a satisfactory explanation of the totality of the effects. It will therefore be good if we carry out our plan to thoroughly investigate the induction phenomena connected with it.

I have ordered a rheostat and a tangent galvanometer, the former in the form in which Prof. Poggendorff has already used it for scientific investigations, the latter as Prof. Dove is using it. (The dimensions of the tangent galvanometer are somewhat different from those of Bunsen’s one, but I have had no reason to modify them, as they have proven to be suitable). As you wished, I am informing you that the rheostat cost 19 Thaler and the tangent galvanometer 12 Thal. I am considering bringing some other apparatus with me as well.

For the sake of completeness I note that pinite was not to be had. Lepidolite does not exist in crystallised form. – Rubellite is a kind of tourmaline. Zircon is unusable for our purpose. You have corundum in sapphire. – There are no antimony and arsenic crystals in suitable size. There were just as [few] copper crystals.

Plücker is supposed to have 2 sorts of topaz, of which he considers one to be [negative] and the other positive. People are engaged with magnetic and diamagnetic investigations in Venice now too, as I see from a paper which has just been sent to me as a gift by Zantedeschi.¹⁰

It would be very gratifying for me if you were so kind as to inform me whether the minerals have arrived safely, and what results you then obtained [with them].

I am happy to supply you with anything else or to give you information, as far as this is at all possible. I ask that only you communicate your wishes to me as soon as possible.

I ask you to send my greetings to my hosts (Gutmann), and to tell you that Herr Krämer, whom you had given me a letter to take to, died some weeks ago, which is why I could give the letter only to his wife.

With best greetings to you and my other friends in Marburg.

entirely Yours

Herm. Knoblauch.

I join 2 [1 word illegible] crystals:

• Heulandite (from the Fassa Valley¹¹) (red, containing iron)

• " " " (from Iceland) (white, without iron).

cleavage parallel to the ‘sloping face’.

_______

It appears to me of a peculiar interest to compare with each other

1) antimony and stibnite ore.

2) arsenic of lead and apatite.

3) hornblende " tremolite.

4) augite " diopside

5) spinel " gahnite

6) 2 sorts of heulandite.

they have [respectively] the same crystalline form (same cleavages) but different chemical constitution. Don’t confound the diff. crystals and keep them until I return; because I wish to see the experiments.

The lectures at the Berlin university are not closed before the end of this week. – My father, who regrets that you have not accompanied me, sends you his best compliments. After the close of the lectures you would have no profit here (as I believe), especially I am afraid you would have no opportunity of working in a laboratory.