Dans cette thèse nous explorons les aspects de la gravité d'Einstein qui sont propres à la dimension quatre.L'une des propriétés surprenantes liées à cette dimension est la possibilité de formuler la gravité de manière 'Chirale'. Dans ce type de reformulations, typiquement, la métrique perd son rôle centrale. La correspondance entre espace-temps et espace des twisteurs est un autre aspect propre à la dimension quatre. Ces formulations, Chirale et Twistorielle, semblent très différentes. Dans la première partie de cette thèse nous montrons qu'elles sont en fait intimement liées: en particulier nous proposons une nouvelle preuve du `théorème du graviton non-linéaire', due à Penrose, dont le cœur est la géométrie des SU(2)-connections (plutôt qu'une métrique). Dans la seconde partie de cette thèse nous montrons que la gravité en trois et quatre dimensions est liée à des théories d'une nature complètement différentes en dimension six et sept. Ces théories, due à Hitchin, sont des théories de trois-formes différentielles invariantes sous difféomorphismes. En dimensions sept, nous rencontrons seulement un succès partiel puisque la théorie 4D qui en résulte est une version modifiée de la gravité. Cependant nous prouvons au passage que les solutions d'une déformation particulière de la gravité ont, en 7D, l’interprétation de variétés avec holonomies G2.Par contre, en réduisant la théorie de six à trois dimensions nous obtenons précisément la gravité 3D. Nous présentons aussi de nouvelles fonctionnelles pour les formes différentielles en six dimensions. Toutes sont invariantes sous difféomorphismes et deux d’entre elles sont topologiques. / In this thesis we take Einstein theory in dimension four seriously, and explore the special aspects of gravity in this number of dimension.Among the many surprising features in dimension four, one of them is the possibility of `Chiral formulations of gravity' - they are surprising as they typically do not rely on a metric. Another is the existence of the Twistor correspondence. The Chiral and Twistor formulations might seems different in nature. In the first part of this thesis we demonstrate that they are in fact closely related. In particular we give a new proof for Penrose's `non-linear graviton theorem' that relies on the geometry of SU(2)-connections only (rather than on metric).In the second part of this thesis we describe partial results towards encoding the full GR in the total space of some fibre bundle over space-time. We indeed show that gravity theory in three and four dimensions can be related to theories of a completely different nature in six and seven dimension respectively. This theories, first advertised by Hitchin, are diffeomorphism invariant theories of differential three-forms.Starting with seven dimensions, we are only partially succesfull: the resulting theory is some deformed version of gravity. We however found that solutions to a particular gravity theory in four dimension have a seven dimensional interpretation as G2 holonomy manifold. On the other hand by going from six to three dimension we do recover three dimensional gravity. As a bonus, we describe new diffeomorphism invariant functionnals for differential forms in six dimension and prove that two of them are topological.

This study focuses on the role and contribution of women in the context of the social and economic development of two towns in Hertfordshire during the nineteenth century. Although the age saw an increase in urbanisation, Hertfordshire remained an agricultural county with long established land owners, a middle class with influence in the towns and its closeness to London attracting the newly wealthy in search of a country estate. The towns selected for this study, Hertford and Hitchin, changed little in their character and, compared with others which experienced industrial expansion, saw a modest population growth. This, however, brought the consequential pressures on housing and poverty. This research is unique in combining the study of the activities of women and the challenges faced by two market towns over a period of time of change and thus making a contribution to the debate on the concept of “separate spheres” by demonstrating that women had a place in the public arena. The daily life of a country town was reliant on a thriving economic environment. As this research demonstrates, many women had trades and businesses, contributed to good causes and were central to the education of children and adults. Their philanthropic efforts supported the building and maintenance of churches, schools, and hospitals. It charts the role of ordinary women, operating in a small town environment, before extension of the suffrage and Equal Opportunities legislation established their position as legitimate influencers of policy and practice. Little work has been done on how the English small town coped with its growth in population and the summons from central government on compliance with an increasing body of legislation on how the town should be run. It was men who undertook the necessary offices associated with this seed of local government but a micro-history of the people who inhabited these two towns demonstrates that women made a significant contribution to social and economic life of these towns.

This research presents a regional study of the implementation of the 1834 Poor Law Amendment Act (commonly known as the New Poor Law) and its operation in Hertfordshire up to 1847. It examines the economic costs of poor relief across the whole of this rural southern county but it also adopts a microhistory approach to examine in detail how the New Poor Law was implemented and administered in four poor law unions: Hatfield, Hitchin, St Albans and Watford. This study makes national and intra-county comparisons of poor relief data, policy and practice. This research focuses on people as well as place and examines how different groups influenced poor law policy and practice. It makes an important finding about the role played by the second Marquis of Salisbury (a prominent Hertfordshire resident) in the review of the poor laws and the legislation that followed. At the local level this thesis explores the process of implementation and gives new emphasis to the contribution made by the assistant poor law commissioners to both process and policy in the initial years of the New Poor Law. This study is unusual in the attention given to the middlemen of the poor law machinery - the poor law guardians and poor law officers including: medical officers, workhouse masters, relieving officers and schoolmasters and mistresses. This detailed examination of the local guardians challenges the existing historiography on the social demography of this body of men, demonstrates that the influence of elite personnel persisted and adds new data to support the argument that the operation of the poor laws was not just regionally but locally diverse. The workhouse, so symbolic of the New Poor Law and an essential component of the deterrent ideology, is considered in the context of attitudes around its construction and capacity as well as its everyday operation. This thesis adds to the poor law historiography with new data on a previously under-researched area of the country; it provides new information on the development of poor law policy, but more importantly it draws attention to the role of the middlemen and how their individual contributions influenced poor law policy and practice.