14 Mr. A. Kennedy's Observations upon 



the aether resists compression to be so great that in the mo- 

 tions producing light it may be regarded as incompressible, 

 the differences A ^ vanish, and the last two of our general 

 equations (3.) of vol. viii., p. 9, become the same as the equa- 

 tions (1.) of this paper. 



The reason assigned by Mr. Kelland (vol. ix. p. S^ 1 .) why 

 the displacements ^are insensible, or, in other words, why 

 there is no vibration in the direction of transmission, cannot, 

 1 conceive, be the true one; because it implies a state of 

 unstable equilibrium. (See Pratt's Mechanical Philosophy, 

 art. 508.) I believe the ingenious Fresnel considered the 

 true reason to be the one which we have just supposed. 



in. Observations upon the (Economy of several Species of 

 Hymeno}itera found in a Garden at Clapton, By A. 

 Kennedy, Esq,^ 

 p-TAVING had leisure this spring and summer to devote 

 ^^ more time than usual to my favourite pursuit, entomo- 

 logy, 1 have paid considerable attention to the oeconomy of 

 various insects inhabiting a summer-house in my father's 

 grounds, made of the stumps of trees, and having a thatched 

 roof, which has afforded me much amusement from the num- 

 ber of different species oi Hymenoptera which nidificate either 

 in the posts or thatch. 



The following is a list of the insects I have observed, and 

 I shall make a few remarks upon the ceconomy of each species, 

 some of the facts relating to which I believe have not before 

 been recorded. 



Fam. DiPLOLEPiDiE. 11. Pemphredon raorio, VanL. 



1. Cratomus megacephalus, JF'. 12. unicolor, ia/. 



Fam. SAPYGiDiE. 13. Psenatratum, Pz. 



2. Sapyga 4-guttata, F. Fam. Vespid^. 



14. Odynerus quadratus, Don. 

 Fam. Crabronid^. 15 bidens, L. 



3. Trypoxylon figulus, Lat, „ 



A.— clavicemm, 5-^ i?'. ,^ „ , Fam. Andrenid^. 



5. Crabro spinipectus. Shuck. ? ^^' "ylaeus signatus, Pz. 



6. Stigmus troglodytes, Van L. Fam. kviDM. 



7. Diodontus insignis, VanL. 17. Chelostoma florisomnis, L, 



8. gracilis, Curt. 18. Osmia bicornis, L. 



9. corniger, Shuck. 19. spinulosa, JC. 



10. Pemphredon liigubris, F. 20. Heriades campanularum, K. 



1. Cratomus megacephalus, Fab. 

 I have observed four or five specimens of this insect settling 



• Commuiiicated by the Author. 



