442 W. A. Norton — Experiments on Contact Resistance. 



also with the nickeliferous iron found in both the stoney and 

 metallic meteoritevs; and furthermore, that this carbonaceous 

 matter contains curious crystalline products soluble in ether 

 and sulphide of carbon, which last have been traced in the gra- 

 phite nodules in the interior of the metallic meteorites. More- 

 over in these graphite nodules we have found magnesia, which 

 is so uniformly a constituent of the minerals of the stoney 



So far then as our present knowledge goes, we know of celes- 

 tial carbon in three conditions, viz : in the gaseous form as 

 detected by the spectroscope in the attenuated matter of comets ; 

 in meteorites in the solid form, impalpable in its nature and 

 diffused in small quantities through pulverulent masses of 

 mineral matter that come to the earth from celestial regions ; 

 also in the solid form, hut compact and hard, resembling terres- 

 trial graphite, and this is imbedded in metallic matter that 

 comes from regions in space. But while we speak of these as 

 forms of carbon, I think we should be careful in associating it 

 in our minds with the element carbon as we understand it in its 

 pure state whether crystallized or amorphous, for I cannot 

 reconcile the carbon vapor detected in comets as simply that 

 known as pure carbon in the form of an elastic vapor, nor are 

 we to circumscribe ourselves with the notion that this cosmical 

 carbon has an organic origin. 



The researches embraced in this communication, while in 

 many respects of a novel character, are imperfect from their 

 very nature, both from lack of material for a thorough and com- 

 plete study, as well as from the present imperfect methods of 

 operating upon a minute quantity of the most interesting of 

 the substances obtained. 



I have therefore detailed as carefully as I could all the results 

 as they have developed themselves, hoping that future oppor- 

 tunities may be afforded for continuing them, when new celes- 

 tial messengers of the carbonaceous type shall visit our globe. 



Art. Ha^ II.— Results 

 Pr 



[Read before the National Academy of Sciences, April 21, 1876.] 

 The experiments here referred to were undertaken with the 

 view of determining the law of the diminution of the minute 

 distance between two surfaces in contact, with the increase of 

 the contact pressure ; and its dependence on the extent, condition 

 and nature of the surfaces in contact Eectangular piec^ ot 

 various substances \ inch in thickness, { inch in width, and oi 



