The SPARC tokamak is a critical next step towards commercial fusion energy. SPARC is designed as a high-field ($B_0 = 12.2$ T), compact ($R_0 = 1.85$ m, $a = 0.57$ m), superconducting, D-T tokamak with the goal of producing fusion gain $Q>2$ from a magnetically confined fusion plasma for the first time. Currently under design, SPARC will continue the high-field path of the Alcator series of tokamaks, utilizing new magnets based on rare earth barium copper oxide high-temperature superconductors to achieve high performance in a compact device. The goal of $Q>2$ is achievable with conservative physics assumptions ($H_{98,y2} = 0.7$) and, with the nominal assumption of $H_{98,y2} = 1$, SPARC is projected to attain $Q \approx 11$ and $P_{\textrm {fusion}} \approx 140$ MW. SPARC will therefore constitute a unique platform for burning plasma physics research with high density ($\langle n_{e} \rangle \approx 3 \times 10^{20}\ \textrm {m}^{-3}$), high temperature ($\langle T_e \rangle \approx 7$ keV) and high power density ($P_{\textrm {fusion}}/V_{\textrm {plasma}} \approx 7\ \textrm {MW}\,\textrm {m}^{-3}$) relevant to fusion power plants. SPARC's place in the path to commercial fusion energy, its parameters and the current status of SPARC design work are presented. This work also describes the basis for global performance projections and summarizes some of the physics analysis that is presented in greater detail in the companion articles of this collection.

Plasma terminating disruptions in tokamaks may result in relativistic runaway electron beams with potentially serious consequences for future devices with large plasma currents. In this paper, we investigate the effect of plasma elongation on the coupled dynamics of runaway generation and resistive diffusion of the electric field. We find that elongated plasmas are less likely to produce large runaway currents, partly due to the lower induced electric fields associated with larger plasmas, and partly due to direct shaping effects, which mainly lead to a reduction in the runaway avalanche gain.

I have just noticed Prof. Webster's note an the tomb of Thomas Say, and it may be of interest to your readers to know that I have recently visited New Harmony, Ind., and met Mr. John Crobin, the owner of the old Maclure home, where stands the tomb of the father of American descriptive entomology. Mr. Corbin, as Prof. Webster states, is much interested in the proper preservation of this tomb, and is much interested also in the history of Thomas Say. In fact, I found many people in the little village of New Harmony who knew about Say, and who were distinctly of the opinion that his residence in their village sheds lustre on its history. The village library is an admirable one, housed in a beautiful building, and among the treasures of the library are certain of Say's manuscripts, among others, one written upon the day of his death.

During the summer of 1879, while working with Professor Comstock upon the natural enemies of the cotton worm, I came across the following passage in his fleld notes of the previous year :—

“August 27.–I found yesterday a cotton worm about five-eighths of an inch in length, which, though yet alive, was being destroyed by three green larvæ which were upon it. I found the specimens abont 10 a. m. Last evening I observed that the cotton worm was nearly eaten. The parasites had very short bodies, which, when they moved, were pointed at one end. I had intended to describe the specimens, but I find that they have spun cocoons about their bodies.

I recently received from Mr. T. D A. Cockerell, Las Cruces, New Mexico, a minute parasite of a Ceroplastes on Euphorbia hypericifolia from the Red Hill district of Jamaica, which was transmitted to him by Dr. M. Grabham. Both genus and species prove to be new, and are printed separately, partly for the reason that my revision of the Aphelininæ of North America has recently been published and I do not expect to do any extensive work on the subfamily again for some time, and partly for the reason that Mr. Cockerell wishes to use the names in the Journal of the Institute of Jamaica.

In the summer of 1889, while engaged in an investigation of the habits and life-history of the horn fly of cattle (Haematobia serrata), the writer at various times brought to Washington from different points in Virginia, large quantities of cow-manure collected in the field, and eventually succeeded in working out the complete life-history of the horn fly, as displayed in Insect Life, Vol. II., No.4, October, 1889. In this article the statement is made, in concluding, that the observations were greatly hindered and rendered difficult by the fact that fresh cow-dung is the nidus for a number of species of Diptera, some about the same size and general appearance as the horn fly, and that no less than twenty distinct species of flies had been reared from horse- and cow-dung, mainly the latter, and six species of parasitic insects as well.

Sir,—I am much interested in Mr. Slingerland's note on the new popular name for Clisiocampa disstria in the Canadian Entomologist for January. I once wrote an editorial for “Insect Life” on popular names (Vol. VII., pp. 363, 364), in which I gave utterance to a certain distaste for “book names” and to a preference for the popular name which grows up among the people. Such names are rarely specifically distinctive, but they are usually catchy, frequently phonetic, and more or less descriptive.

An interesting interference in the adoption of the generic name Rileya has recently taken place between Mr.Ashmead and myself, and as I am of the opinion that this name should apply to the genus of Encyrtinæ defined by myself, rather than to the genus of Eurytominæ defined by Mr. Ashmead, I state in this note the circumstances of the interference, and print in full the paper in which my description occurred.

The Chalcidid subfamily Trichogrammatinae is composed entirely of species parasitic in the eggs of other insects. A synopsis of the genera has recently been published by Dr.Chr. Aurivillius in “Entomologisk Tidskrift,” for 1897, pp.249–256, apropos to the establishment of a new genus (Oophthora) for a species which he has reared in Sweden from the eggs of Semblidis lutariae. In this synopsis of the genera Dr. Aurivillius makes Lathromeris, Förster (Hymenopt. Stud., 1856, 2, pp. 87–89) a synonym of Chaetostricha, Haliday (An. and Mag. Nat. Hist. Ser. 2, Vol. 7, 1851, p.212).

Without entering further into the discussion of priority, beyond stating that Mr. Ashmead is wrong in the points(1), that my original communication was read after the publication of his synoptical table, (it was read two days before the receipt of the number of Entomologica Americana, in which the table was published), and (2), that his full description was published before mine; (mine was published nine days before the receipt of the Kansas bulletin).