1867] On the Physical Constitutio?i of the Sun and Stars. 25 



equal development witli the lateral lobes lead to the inference that this 

 central part is present from the earliest period, and that the thyroid 

 isthmus is not formed by a growing together of two distinct sidepieces. 

 In examining the thyroid in fcetal dogs, cats, and hares, I have always 

 found the middle portion equally developed with the side lobes, and 

 bounded by notches which seem to define it from them. With the growth 

 of the foetus the central part appears to flatten, losing the rounded, 

 lobular condition, and sometimes disappears. The isthmus is formed 

 from the smaller, middle, division uniting'the other two ; but there may be 

 an absence of isthmus through failure of this union, the middle portion 

 joining the right or left lobe, or a small middle lobe may remain distinct 

 from the other two. The pyramid is very commonly met with in the 

 foetus, and is clearly an outlying part of the body, sometimes represented 

 by bud-like projections, sometimes consisting of a process which reaches 

 to the hyoid bone. It is probable that these outgrowths from the foetal 

 thyroid often shrink and disappear with advancing years. 



The dissections of the human foetus lead to the following conclu- 

 sions : — (1) The thyroid is developed in connexion with the air-tube, 

 and has no relation with the thymus. (2) It does not consist of two 

 separate lateral masses, and the isthmus is present from the first as 

 a distinct central portion. (3) The pyramid is an outlying part of 

 the body, presenting, during foetal life, all possible variations as to shape 

 and site. 



V. " On the Physical Constitution of the Sun and Stars/^ By G. 

 Johnstone Stoney, M.A., F.R.S., F.R.A.S., Secretary to the 

 Queen^s University in Ireland. Received May 15, 1867. 



(Abstract.) 



An attempt is made in the memoir of which this is an abstract to take 

 advantage of the insight we have gained within the last few years into the 

 molecular constitution of gases, and the laws which regulate the exchanges 

 of heat that take place between bodies placed in presence of one another, 

 and to apply these new materials to the interpretation of the phenomena of 

 the photosphere of the sun, the appearances presented during total eclipses, 

 and the information about both sun and stars given by the spectroscope. 



In an inquiry like this, where we are obliged to put up with such proofs as 

 the materials at our disposal can supply, we must be content to accept re- 

 sults of every variety of probability, from that degree, bordering upon cer- 

 tainty, which commands an unhesitating assent, to that of which the chief 

 scientific value is that it prompts to further investigation and points out a 

 path. Those who read the memoir itself will best judge of the probability 

 of each conclusion from the proofs laid before them ; but in this sketch of 

 its contents it may not be useless to indicate what is the value put upon 



