Royal Society. 309 



cular valves, it is noticed that a considerable portion of tendinous 

 fibres pass from the insertions of the cords, through the valves, to 

 the zones, and many of the smaller cords pass up directly into the 

 angle formed between the under surface of the valve and the inner 

 surface of the ventricle, and at once enter into the formations of the 

 fibrous zones. These cords are short, and many of them spring from 

 the wall of the ventricle, behind the valve. Therefore it results, 

 that these zones are densest and most strongly marked in those 

 portions corresponding to the attached borders of the valves, and 

 gradually become less distinct towards the intervals between them. 

 Hence the greater portion of the auriculo-ventricular zones is more 

 properly to be considered in connexion with the valves. 



The fibres of elastic tissue exist in the auriculo-ventricular valves, 

 but more sparingly than in the arterial valves. 



The many contradictor}' statements which have been advanced 

 concerning the existence of muscular fibres in the auriculo-ventri- 

 cular valves, may perhaps be explained by a consideration of the 

 mode in which the muscular fibres of the auricles terminate, which 

 has been already described. The internal fibres which have been 

 mentioned, descending from the auricular walls into the valves just 

 beyond their attached margins, may be traced to a greater distance 

 in some cases than in others. They generally terminate by a tole- 

 rably well-defined margin, but this varies. They usually descend 

 for a greater distance between the layers of the anterior mitral valve, 

 immediately beneath its auricular surface ; but even here they are 

 seldom found stretching far into the valve, not terminating, however, 

 so abruptly. 



Therefore, if a portion of the attached border of a valve imme- 

 diately below its upper surface be examined, muscular fibres in 

 abundance will generally be detected ; whereas if sought for in any 

 other portion of the valve far from its attached border, according to 

 the foregoing observations, they will not be found. 



March 25, 1852. — The following paper was read: — Experimental 

 Researches in Electricity. Twenty-ninth Series. By Michael 

 Faraday, Esq., D.C.L., F.R.S. &c. 



In the present series of researches the author endeavours in the 

 first place to establish the principles he announced in the last, with 

 regard to the definite character of the lines of magnetic force, by 

 results obtained experimentally with the magnetic force of the earth. 

 For this purpose he reverts to the thick wire galvanometer before 

 described, and points out the precautions respecting the cleanliness 

 of the coils, the thickness and shortness of the conductors, the per- 

 fect contacts, effected either by soldering or cups of mercury ; and 

 marks the value of double observations, i. e. observations afforded 

 on both sides of zero. The nature of the impulse on the needles is 

 pointed out ; being not that of a constant current for a limited or 

 unlimited time, but of a given amount of electricity exerted, cither 

 regularly or irregularly, within a short period ; and it is shown ex- 

 perimentally that such impulses produce equal results of deflection, 

 and also that when two or more such impulses are given within a 

 limited time, the whole arc of swing is nearly proportional to their 



