498 Proceedings of the Royal Society 
ellipsoid of given form, and from this to reduce a measure of the 
dielectric strength of air. Some curious problems of mathematical 
physics arise here in connection with the assumption of varying 
specific inductive capacity, which I can only mention in passing. 
I find on a certain rough assumption that ovary ellipsoids of reason- 
able dimensions ought to give practically measurable results, and 
propose to try the experiment. 
With the same end in view I think it would he desirable to 
reduce the experiment of Bailie and others with spheres, in cases 
where the surface density can he calculated, and to examine the 
values of the dielectric strength in these cases. Until this or some- 
thing equivalent is done, it is clear that we have really no experimental 
ground for asserting the existence of such a constant as the 
dielectric strength of a medium, and therefore cannot take the very 
first step towards a physical theory of the disruptive discharge, 
which appears to me to be the next great advance to he made in the 
science of electricity. 
4. Diagnoses plantarum novarum et imperfecte descriptarum 
Fhanerogamarum Socotrensium ; quas elaboravit Bayley 
Balfour, Scientise Doctor et in Universitate Glascuensi 
rerum botanicarum regius professor. Pars Prima. 
Plena descriptio Botanices Socotrensis quantum nobis cognitse, 
brevi tempore subjicietur Societati Regiae Edinensis ut in suis Actis 
in lucem emittatur et divulgetur. Quoniam verum spatio certo 
temporis opus erit ut singulae partes et minutiae Florae tarn abun- 
dantis et copiosae plene elaborentur et perlustrentur, et quoniam 
perplures formae endemicae tam generum quam specierum in ea 
Flora comprehenduntur, oportet et congruit opportunis temporis 
intervallis, opere progrediente, breves diagnoses novarum plantarum 
in medium proponere, ut prioritas vindicetur no minibus quae his 
novis tribuantur, et quae in volumine Actorum Societatis Regiae 
publice emittentur. 
Kune igitur in medium profero aliquas diagnoses novorum 
generum et specierum. In hac parte prima plantas novas Dicotyle- 
donearum Polypetalasarum solum descripsi ; in partibus subse- 
