How can one study the absence of knowledge, the voids, the conscious and unconscious unknowns through history? Investigations into late medieval and early modern practices of measuring, of risk calculation, of ignorance within financial administrations, of conceiving the docta ignorantia as well as the silence of the illiterate are combined with contributions regarding knowledge gaps within identification procedures and political decision-making, with the emergence of consciously delimited blanks on geographical maps, with ignorance as a factor embedded in iconographic programs, in translation processes and the semantic potentials of reading. Based on thorough archival analysis, these selected contributions from conferences at Harvard and Paris are tightly framed by new theoretical elaborations that have implications beyond these cases and epochal focus. Contributors: Giovanni Ceccarelli, Taylor Cowdery, Lucile Haguet, John T. Hamilton, Lucian Hölscher, Moritz Isenmann, Adam J. Kosto, Marie-Laure Legay, Andrew McKenzie-McHarg, Fabrice Micallef, William T. O ́Reilly, Eleonora Rohland, Mathias Schmoeckel, Daniel L. Smail, Govind P. Sreenivasan, and Cornel Zwierlein.

Gösta Mittag-Leffler (1846–1927) played a significant role as both a scientist and entrepreneur. Regarded as the father of Swedish mathematics, his influence extended far beyond his chosen field because of his extensive network of international contacts in science, business, and the arts. He was instrumental in seeing to it that Marie Curie was awarded the Nobel Prize twice. One of Mittag-Leffler’s major accomplishments was the founding of the journal Acta Mathematica , published by Institut Mittag-Leffler and Sweden’s Royal Academy of Sciences. Arild Stubhaug’s research for this monumental biography relied on a wealth of primary and secondary resources, including more than 30000 letters that are part of the Mittag-Leffler archives. Written in a lucid and compelling manner, the biography contains many hitherto unknown facts about Mittag-Leffler’s personal life and professional endeavors. It will be of great interest to both mathematicians and general readers interested in science and culture.

This title is part of UC Press's Voices Revived program, which commemorates University of California Press’s mission to seek out and cultivate the brightest minds and give them voice, reach, and impact. Drawing on a backlist dating to 1893, Voices Revived makes high-quality, peer-reviewed scholarship accessible once again using print-on-demand technology. This title was originally published in 1955.

The Sun is nowadays observed using di?erent techniques that provide an almost instantaneous 3-D map of its structure. Of particular interest is the studyofthevariabilityinthesolaroutputproducedbythedissipationofm- netic energy on di?erent spatial and temporal scales – the so-called magnetic activity. The 11-year cycle is the main feature describing this phenomenon. Apart from its intrinsic scienti?c interest, this topic is worth studying because of the interaction of such processes with the terrestrial environment. A ?eet of space and ground-based observatories are currently monitoring the behaviour of our star on a daily basis. However, solar activity varies not only on this decadal time-scale, as has been attested mainly through two methods: (a) records of the number of sunspots observed on the solar surface from 1610, and (b) the records of 14 10 cosmogenic isotopes, such as Cand Be, measured in tree-rings and i- cores, respectively. The study of the long-term behaviour of solar activity may be comp- mented by the study of historical accounts describing phenomena directly or indirectly related to solar activity. Numerous scienti?c and non-scienti?c d- uments have reported these events and we can make use of them as a proxy of solar activity in past times.